diff --git a/test/spec/read-write-concern/README.rst b/test/spec/read-write-concern/README.rst
new file mode 100644
index 0000000000..5995590136
--- /dev/null
+++ b/test/spec/read-write-concern/README.rst
@@ -0,0 +1,80 @@
+=======================
+Connection String Tests
+=======================
+
+The YAML and JSON files in this directory tree are platform-independent tests
+that drivers can use to prove their conformance to the Read and Write Concern 
+specification.
+
+Version
+-------
+
+Files in the "specifications" repository have no version scheme. They are not
+tied to a MongoDB server version.
+
+Format
+------
+
+Connection String
+~~~~~~~~~~~~~~~~~
+
+These tests are designed to exercise the connection string parsing related
+to read concern and write concern.
+
+Each YAML file contains an object with a single ``tests`` key. This key is an
+array of test case objects, each of which have the following keys:
+
+- ``description``: A string describing the test.
+- ``uri``: A string containing the URI to be parsed.
+- ``valid:``: a boolean indicating if parsing the uri should result in an error.
+- ``writeConcern:`` A document indicating the expected write concern.
+- ``readConcern:`` A document indicating the expected read concern.
+
+If a test case includes a null value for one of these keys, or if the key is missing,
+no assertion is necessary. This both simplifies parsing of the test files and allows flexibility
+for drivers that might substitute default values *during* parsing.
+
+Document
+~~~~~~~~
+
+These tests are designed to ensure compliance with the spec in relation to what should be 
+sent to the server.
+
+Each YAML file contains an object with a single ``tests`` key. This key is an
+array of test case objects, each of which have the following keys:
+
+- ``description``: A string describing the test.
+- ``valid:``: a boolean indicating if the write concern created from the document is valid.
+- ``writeConcern:`` A document indicating the write concern to use.
+- ``writeConcernDocument:`` A document indicating the write concern to be sent to the server.
+- ``readConcern:`` A document indicating the read concern to use.
+- ``readConcernDocument:`` A document indicating the read concern to be sent to the server.
+- ``isServerDefault:`` Indicates whether the read or write concern is considered the server's default.
+- ``isAcknowledged:`` Indicates if the write concern should be considered acknowledged.
+
+Operation
+~~~~~~~~~
+
+These tests check that the default write concern is omitted in operations.
+
+The spec test format is an extension of `transactions spec tests <https://github.com/mongodb/specifications/blob/master/source/transactions/tests/README.rst>`_ with the following additions:
+
+- ``writeConcern`` in the ``databaseOptions`` or ``collectionOptions`` may be an empty document to indicate a `server default write concern <https://github.com/mongodb/specifications/blob/master/source/read-write-concern/read-write-concern.rst#servers-default-writeconcern>`_. For example, in libmongoc:
+
+    .. code:: c
+
+       /* Create a default write concern, and set on a collection object. */
+       mongoc_write_concern_t *wc = mongoc_write_concern_new ();
+       mongoc_collection_set_write_concern (collection, wc);
+
+    If the driver has no way to explicitly set a default write concern on a database or collection, ignore the empty ``writeConcern`` document and continue with the test.
+- The operations ``createIndex``, ``dropIndex`` are introduced.
+
+
+Use as unit tests
+=================
+
+Testing whether a URI is valid or not should simply be a matter of checking
+whether URI parsing raises an error or exception.
+Testing for emitted warnings may require more legwork (e.g. configuring a log
+handler and watching for output).
diff --git a/test/spec/read-write-concern/connection-string/read-concern.json b/test/spec/read-write-concern/connection-string/read-concern.json
new file mode 100644
index 0000000000..1ecad8c268
--- /dev/null
+++ b/test/spec/read-write-concern/connection-string/read-concern.json
@@ -0,0 +1,47 @@
+{
+  "tests": [
+    {
+      "description": "Default",
+      "uri": "mongodb://localhost/",
+      "valid": true,
+      "warning": false,
+      "readConcern": {}
+    },
+    {
+      "description": "local specified",
+      "uri": "mongodb://localhost/?readConcernLevel=local",
+      "valid": true,
+      "warning": false,
+      "readConcern": {
+        "level": "local"
+      }
+    },
+    {
+      "description": "majority specified",
+      "uri": "mongodb://localhost/?readConcernLevel=majority",
+      "valid": true,
+      "warning": false,
+      "readConcern": {
+        "level": "majority"
+      }
+    },
+    {
+      "description": "linearizable specified",
+      "uri": "mongodb://localhost/?readConcernLevel=linearizable",
+      "valid": true,
+      "warning": false,
+      "readConcern": {
+        "level": "linearizable"
+      }
+    },
+    {
+      "description": "available specified",
+      "uri": "mongodb://localhost/?readConcernLevel=available",
+      "valid": true,
+      "warning": false,
+      "readConcern": {
+        "level": "available"
+      }
+    }
+  ]
+}
diff --git a/test/spec/read-write-concern/connection-string/read-concern.yml b/test/spec/read-write-concern/connection-string/read-concern.yml
new file mode 100644
index 0000000000..499405fbae
--- /dev/null
+++ b/test/spec/read-write-concern/connection-string/read-concern.yml
@@ -0,0 +1,32 @@
+tests:
+    -
+        description: "Default"
+        uri: "mongodb://localhost/"
+        valid: true
+        warning: false
+        readConcern: { }
+    -
+        description: "local specified"
+        uri: "mongodb://localhost/?readConcernLevel=local"
+        valid: true
+        warning: false
+        readConcern: { level: "local" }
+    -
+        description: "majority specified"
+        uri: "mongodb://localhost/?readConcernLevel=majority"
+        valid: true
+        warning: false
+        readConcern: { level: "majority" }
+    -
+        description: "linearizable specified"
+        uri: "mongodb://localhost/?readConcernLevel=linearizable"
+        valid: true
+        warning: false
+        readConcern: { level: "linearizable" }
+    -
+        description: "available specified"
+        uri: "mongodb://localhost/?readConcernLevel=available"
+        valid: true
+        warning: false
+        readConcern: { level: "available" }
+        
diff --git a/test/spec/read-write-concern/connection-string/write-concern.json b/test/spec/read-write-concern/connection-string/write-concern.json
new file mode 100644
index 0000000000..51bdf821c3
--- /dev/null
+++ b/test/spec/read-write-concern/connection-string/write-concern.json
@@ -0,0 +1,118 @@
+{
+  "tests": [
+    {
+      "description": "Default",
+      "uri": "mongodb://localhost/",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {}
+    },
+    {
+      "description": "w as a valid number",
+      "uri": "mongodb://localhost/?w=1",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {
+        "w": 1
+      }
+    },
+    {
+      "description": "w as an invalid number",
+      "uri": "mongodb://localhost/?w=-2",
+      "valid": false,
+      "warning": null
+    },
+    {
+      "description": "w as a string",
+      "uri": "mongodb://localhost/?w=majority",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {
+        "w": "majority"
+      }
+    },
+    {
+      "description": "wtimeoutMS as a valid number",
+      "uri": "mongodb://localhost/?wtimeoutMS=500",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {
+        "wtimeoutMS": 500
+      }
+    },
+    {
+      "description": "wtimeoutMS as an invalid number",
+      "uri": "mongodb://localhost/?wtimeoutMS=-500",
+      "valid": false,
+      "warning": null
+    },
+    {
+      "description": "journal as false",
+      "uri": "mongodb://localhost/?journal=false",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {
+        "journal": false
+      }
+    },
+    {
+      "description": "journal as true",
+      "uri": "mongodb://localhost/?journal=true",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {
+        "journal": true
+      }
+    },
+    {
+      "description": "All options combined",
+      "uri": "mongodb://localhost/?w=3&wtimeoutMS=500&journal=true",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {
+        "w": 3,
+        "wtimeoutMS": 500,
+        "journal": true
+      }
+    },
+    {
+      "description": "Unacknowledged with w",
+      "uri": "mongodb://localhost/?w=0",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {
+        "w": 0
+      }
+    },
+    {
+      "description": "Unacknowledged with w and journal",
+      "uri": "mongodb://localhost/?w=0&journal=false",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {
+        "w": 0,
+        "journal": false
+      }
+    },
+    {
+      "description": "Unacknowledged with w and wtimeoutMS",
+      "uri": "mongodb://localhost/?w=0&wtimeoutMS=500",
+      "valid": true,
+      "warning": false,
+      "writeConcern": {
+        "w": 0,
+        "wtimeoutMS": 500
+      }
+    },
+    {
+      "description": "Acknowledged with w as 0 and journal true",
+      "uri": "mongodb://localhost/?w=0&journal=true",
+      "valid": false,
+      "warning": false,
+      "writeConcern": {
+        "w": 0,
+        "journal": true
+      }
+    }
+  ]
+}
diff --git a/test/spec/read-write-concern/connection-string/write-concern.yml b/test/spec/read-write-concern/connection-string/write-concern.yml
new file mode 100644
index 0000000000..ca61085865
--- /dev/null
+++ b/test/spec/read-write-concern/connection-string/write-concern.yml
@@ -0,0 +1,77 @@
+tests:
+    -
+        description: "Default"
+        uri: "mongodb://localhost/"
+        valid: true
+        warning: false
+        writeConcern: { }
+    -
+        description: "w as a valid number"
+        uri: "mongodb://localhost/?w=1"
+        valid: true
+        warning: false
+        writeConcern: { w: 1 }
+    -
+        description: "w as an invalid number"
+        uri: "mongodb://localhost/?w=-2"
+        valid: false
+        warning: ~
+    -
+        description: "w as a string"
+        uri: "mongodb://localhost/?w=majority"
+        valid: true
+        warning: false
+        writeConcern: { w: "majority" }
+    -
+        description: "wtimeoutMS as a valid number"
+        uri: "mongodb://localhost/?wtimeoutMS=500"
+        valid: true
+        warning: false
+        writeConcern: { wtimeoutMS: 500 }
+    -
+        description: "wtimeoutMS as an invalid number"
+        uri: "mongodb://localhost/?wtimeoutMS=-500"
+        valid: false
+        warning: ~
+    -
+        description: "journal as false"
+        uri: "mongodb://localhost/?journal=false"
+        valid: true
+        warning: false
+        writeConcern: { journal: false }
+    -
+        description: "journal as true"
+        uri: "mongodb://localhost/?journal=true"
+        valid: true
+        warning: false
+        writeConcern: { journal: true }
+    -
+        description: "All options combined"
+        uri: "mongodb://localhost/?w=3&wtimeoutMS=500&journal=true"
+        valid: true
+        warning: false
+        writeConcern: { w: 3, wtimeoutMS: 500, journal: true }
+    -
+        description: "Unacknowledged with w"
+        uri: "mongodb://localhost/?w=0"
+        valid: true
+        warning: false
+        writeConcern: { w: 0 }
+    -
+        description: "Unacknowledged with w and journal"
+        uri: "mongodb://localhost/?w=0&journal=false"
+        valid: true
+        warning: false
+        writeConcern: { w: 0, journal: false }
+    -
+        description: "Unacknowledged with w and wtimeoutMS"
+        uri: "mongodb://localhost/?w=0&wtimeoutMS=500"
+        valid: true
+        warning: false
+        writeConcern: { w: 0, wtimeoutMS: 500 }
+    -
+        description: "Acknowledged with w as 0 and journal true"
+        uri: "mongodb://localhost/?w=0&journal=true"
+        valid: false
+        warning: false
+        writeConcern: { w: 0, journal: true }
diff --git a/test/spec/read-write-concern/document/read-concern.json b/test/spec/read-write-concern/document/read-concern.json
new file mode 100644
index 0000000000..187397dae5
--- /dev/null
+++ b/test/spec/read-write-concern/document/read-concern.json
@@ -0,0 +1,66 @@
+{
+  "tests": [
+    {
+      "description": "Default",
+      "valid": true,
+      "readConcern": {},
+      "readConcernDocument": {},
+      "isServerDefault": true
+    },
+    {
+      "description": "Majority",
+      "valid": true,
+      "readConcern": {
+        "level": "majority"
+      },
+      "readConcernDocument": {
+        "level": "majority"
+      },
+      "isServerDefault": false
+    },
+    {
+      "description": "Local",
+      "valid": true,
+      "readConcern": {
+        "level": "local"
+      },
+      "readConcernDocument": {
+        "level": "local"
+      },
+      "isServerDefault": false
+    },
+    {
+      "description": "Linearizable",
+      "valid": true,
+      "readConcern": {
+        "level": "linearizable"
+      },
+      "readConcernDocument": {
+        "level": "linearizable"
+      },
+      "isServerDefault": false
+    },
+    {
+      "description": "Snapshot",
+      "valid": true,
+      "readConcern": {
+        "level": "snapshot"
+      },
+      "readConcernDocument": {
+        "level": "snapshot"
+      },
+      "isServerDefault": false
+    },
+    {
+      "description": "Available",
+      "valid": true,
+      "readConcern": {
+        "level": "available"
+      },
+      "readConcernDocument": {
+        "level": "available"
+      },
+      "isServerDefault": false
+    }
+  ]
+}
diff --git a/test/spec/read-write-concern/document/read-concern.yml b/test/spec/read-write-concern/document/read-concern.yml
new file mode 100644
index 0000000000..7d774752d9
--- /dev/null
+++ b/test/spec/read-write-concern/document/read-concern.yml
@@ -0,0 +1,37 @@
+tests:
+    -
+        description: "Default"
+        valid: true
+        readConcern: {}
+        readConcernDocument: {}
+        isServerDefault: true
+    - 
+        description: "Majority"
+        valid: true
+        readConcern: { level: "majority" }
+        readConcernDocument: { level: "majority" }
+        isServerDefault: false
+    -
+        description: "Local"
+        valid: true
+        readConcern: { level: "local" }
+        readConcernDocument: { level: "local" }
+        isServerDefault: false
+    -
+        description: "Linearizable"
+        valid: true
+        readConcern: { level: "linearizable" }
+        readConcernDocument: { level: "linearizable" }
+        isServerDefault: false
+    -
+        description: "Snapshot"
+        valid: true
+        readConcern: { level: "snapshot" }
+        readConcernDocument: {level: "snapshot" }
+        isServerDefault: false
+    -
+        description: "Available"
+        valid: true
+        readConcern: { level: "available" }
+        readConcernDocument: { level: "available" }
+        isServerDefault: false
diff --git a/test/spec/read-write-concern/document/write-concern.json b/test/spec/read-write-concern/document/write-concern.json
new file mode 100644
index 0000000000..64cd5d0eae
--- /dev/null
+++ b/test/spec/read-write-concern/document/write-concern.json
@@ -0,0 +1,174 @@
+{
+  "tests": [
+    {
+      "description": "Default",
+      "valid": true,
+      "writeConcern": {},
+      "writeConcernDocument": {},
+      "isServerDefault": true,
+      "isAcknowledged": true
+    },
+    {
+      "description": "W as a number",
+      "valid": true,
+      "writeConcern": {
+        "w": 3
+      },
+      "writeConcernDocument": {
+        "w": 3
+      },
+      "isServerDefault": false,
+      "isAcknowledged": true
+    },
+    {
+      "description": "W as an invalid number",
+      "valid": false,
+      "writeConcern": {
+        "w": -3
+      },
+      "writeConcernDocument": null,
+      "isServerDefault": null,
+      "isAcknowledged": null
+    },
+    {
+      "description": "W as majority",
+      "valid": true,
+      "writeConcern": {
+        "w": "majority"
+      },
+      "writeConcernDocument": {
+        "w": "majority"
+      },
+      "isServerDefault": false,
+      "isAcknowledged": true
+    },
+    {
+      "description": "W as a custom string",
+      "valid": true,
+      "writeConcern": {
+        "w": "my_mode"
+      },
+      "writeConcernDocument": {
+        "w": "my_mode"
+      },
+      "isServerDefault": false,
+      "isAcknowledged": true
+    },
+    {
+      "description": "WTimeoutMS",
+      "valid": true,
+      "writeConcern": {
+        "wtimeoutMS": 1000
+      },
+      "writeConcernDocument": {
+        "wtimeout": 1000
+      },
+      "isServerDefault": false,
+      "isAcknowledged": true
+    },
+    {
+      "description": "WTimeoutMS as an invalid number",
+      "valid": false,
+      "writeConcern": {
+        "wtimeoutMS": -1000
+      },
+      "writeConcernDocument": null,
+      "isServerDefault": null,
+      "isAcknowledged": null
+    },
+    {
+      "description": "Journal as true",
+      "valid": true,
+      "writeConcern": {
+        "journal": true
+      },
+      "writeConcernDocument": {
+        "j": true
+      },
+      "isServerDefault": false,
+      "isAcknowledged": true
+    },
+    {
+      "description": "Journal as false",
+      "valid": true,
+      "writeConcern": {
+        "journal": false
+      },
+      "writeConcernDocument": {
+        "j": false
+      },
+      "isServerDefault": false,
+      "isAcknowledged": true
+    },
+    {
+      "description": "Unacknowledged with only w",
+      "valid": true,
+      "writeConcern": {
+        "w": 0
+      },
+      "writeConcernDocument": {
+        "w": 0
+      },
+      "isServerDefault": false,
+      "isAcknowledged": false
+    },
+    {
+      "description": "Unacknowledged with wtimeoutMS",
+      "valid": true,
+      "writeConcern": {
+        "w": 0,
+        "wtimeoutMS": 500
+      },
+      "writeConcernDocument": {
+        "w": 0,
+        "wtimeout": 500
+      },
+      "isServerDefault": false,
+      "isAcknowledged": false
+    },
+    {
+      "description": "Unacknowledged with journal",
+      "valid": true,
+      "writeConcern": {
+        "w": 0,
+        "journal": false
+      },
+      "writeConcernDocument": {
+        "w": 0,
+        "j": false
+      },
+      "isServerDefault": false,
+      "isAcknowledged": false
+    },
+    {
+      "description": "W is 0 with journal true",
+      "valid": false,
+      "writeConcern": {
+        "w": 0,
+        "journal": true
+      },
+      "writeConcernDocument": {
+        "w": 0,
+        "j": true
+      },
+      "isServerDefault": false,
+      "isAcknowledged": true
+    },
+    {
+      "description": "Everything",
+      "valid": true,
+      "writeConcern": {
+        "w": 3,
+        "wtimeoutMS": 1000,
+        "journal": true
+      },
+      "writeConcernDocument": {
+        "w": 3,
+        "wtimeout": 1000,
+        "j": true
+      },
+      "isServerDefault": false,
+      "isAcknowledged": true
+    }
+  ]
+}
diff --git a/test/spec/read-write-concern/document/write-concern.yml b/test/spec/read-write-concern/document/write-concern.yml
new file mode 100644
index 0000000000..bd82fdd59d
--- /dev/null
+++ b/test/spec/read-write-concern/document/write-concern.yml
@@ -0,0 +1,99 @@
+tests:
+    -
+        description: "Default"
+        valid: true
+        writeConcern: {}
+        writeConcernDocument: {}
+        isServerDefault: true
+        isAcknowledged: true
+    -
+        description: "W as a number"
+        valid: true
+        writeConcern: { w: 3 }
+        writeConcernDocument: { w: 3 }
+        isServerDefault: false
+        isAcknowledged: true
+    -
+        description: "W as an invalid number"
+        valid: false
+        writeConcern: { w: -3 }
+        writeConcernDocument: ~
+        isServerDefault: ~
+        isAcknowledged: ~
+    -
+        description: "W as majority"
+        valid: true
+        writeConcern: { w: "majority" }
+        writeConcernDocument: { w: "majority" }
+        isServerDefault: false
+        isAcknowledged: true
+    -
+        description: "W as a custom string"
+        valid: true
+        writeConcern: { w: "my_mode" }
+        writeConcernDocument: { w: "my_mode" }
+        isServerDefault: false
+        isAcknowledged: true
+    -
+        description: "WTimeoutMS"
+        valid: true
+        writeConcern: { wtimeoutMS: 1000 }
+        writeConcernDocument: { wtimeout: 1000 }
+        isServerDefault: false
+        isAcknowledged: true
+    -
+        description: "WTimeoutMS as an invalid number"
+        valid: false
+        writeConcern: { wtimeoutMS: -1000 }
+        writeConcernDocument: ~
+        isServerDefault: ~
+        isAcknowledged: ~
+    -
+        description: "Journal as true"
+        valid: true
+        writeConcern: { journal: true }
+        writeConcernDocument: { j: true }
+        isServerDefault: false
+        isAcknowledged: true
+    -
+        description: "Journal as false"
+        valid: true
+        writeConcern: { journal: false }
+        writeConcernDocument: { j: false }
+        isServerDefault: false
+        isAcknowledged: true
+    -
+        description: "Unacknowledged with only w"
+        valid: true
+        writeConcern: { w: 0 }
+        writeConcernDocument: { w: 0 }
+        isServerDefault: false
+        isAcknowledged: false
+    -
+        description: "Unacknowledged with wtimeoutMS"
+        valid: true
+        writeConcern: { w: 0, wtimeoutMS: 500 }
+        writeConcernDocument: { w: 0, wtimeout: 500 }
+        isServerDefault: false
+        isAcknowledged: false
+    -
+        description: "Unacknowledged with journal"
+        valid: true
+        writeConcern: { w: 0, journal: false }
+        writeConcernDocument: { w: 0, j: false }
+        isServerDefault: false
+        isAcknowledged: false
+    -
+        description: "W is 0 with journal true"
+        valid: false
+        writeConcern: { w: 0, journal: true }
+        writeConcernDocument: { w: 0, j: true }
+        isServerDefault: false
+        isAcknowledged: true
+    -
+        description: "Everything"
+        valid: true
+        writeConcern: { w: 3, wtimeoutMS: 1000, journal: true }
+        writeConcernDocument: { w: 3, wtimeout: 1000, j: true }
+        isServerDefault: false
+        isAcknowledged: true
diff --git a/test/spec/read-write-concern/operation/default-write-concern-2.6.json b/test/spec/read-write-concern/operation/default-write-concern-2.6.json
new file mode 100644
index 0000000000..c623298cd7
--- /dev/null
+++ b/test/spec/read-write-concern/operation/default-write-concern-2.6.json
@@ -0,0 +1,544 @@
+{
+  "data": [
+    {
+      "_id": 1,
+      "x": 11
+    },
+    {
+      "_id": 2,
+      "x": 22
+    }
+  ],
+  "collection_name": "default_write_concern_coll",
+  "database_name": "default_write_concern_db",
+  "runOn": [
+    {
+      "minServerVersion": "2.6"
+    }
+  ],
+  "tests": [
+    {
+      "description": "DeleteOne omits default write concern",
+      "operations": [
+        {
+          "name": "deleteOne",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "filter": {}
+          },
+          "result": {
+            "deletedCount": 1
+          }
+        }
+      ],
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "delete": "default_write_concern_coll",
+              "deletes": [
+                {
+                  "q": {},
+                  "limit": 1
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    },
+    {
+      "description": "DeleteMany omits default write concern",
+      "operations": [
+        {
+          "name": "deleteMany",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "filter": {}
+          },
+          "result": {
+            "deletedCount": 2
+          }
+        }
+      ],
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "delete": "default_write_concern_coll",
+              "deletes": [
+                {
+                  "q": {},
+                  "limit": 0
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    },
+    {
+      "description": "BulkWrite with all models omits default write concern",
+      "operations": [
+        {
+          "name": "bulkWrite",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "ordered": true,
+            "requests": [
+              {
+                "name": "deleteMany",
+                "arguments": {
+                  "filter": {}
+                }
+              },
+              {
+                "name": "insertOne",
+                "arguments": {
+                  "document": {
+                    "_id": 1
+                  }
+                }
+              },
+              {
+                "name": "updateOne",
+                "arguments": {
+                  "filter": {
+                    "_id": 1
+                  },
+                  "update": {
+                    "$set": {
+                      "x": 1
+                    }
+                  }
+                }
+              },
+              {
+                "name": "insertOne",
+                "arguments": {
+                  "document": {
+                    "_id": 2
+                  }
+                }
+              },
+              {
+                "name": "replaceOne",
+                "arguments": {
+                  "filter": {
+                    "_id": 1
+                  },
+                  "replacement": {
+                    "x": 2
+                  }
+                }
+              },
+              {
+                "name": "insertOne",
+                "arguments": {
+                  "document": {
+                    "_id": 3
+                  }
+                }
+              },
+              {
+                "name": "updateMany",
+                "arguments": {
+                  "filter": {
+                    "_id": 1
+                  },
+                  "update": {
+                    "$set": {
+                      "x": 3
+                    }
+                  }
+                }
+              },
+              {
+                "name": "deleteOne",
+                "arguments": {
+                  "filter": {
+                    "_id": 3
+                  }
+                }
+              }
+            ]
+          }
+        }
+      ],
+      "outcome": {
+        "collection": {
+          "name": "default_write_concern_coll",
+          "data": [
+            {
+              "_id": 1,
+              "x": 3
+            },
+            {
+              "_id": 2
+            }
+          ]
+        }
+      },
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "delete": "default_write_concern_coll",
+              "deletes": [
+                {
+                  "q": {},
+                  "limit": 0
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "insert": "default_write_concern_coll",
+              "documents": [
+                {
+                  "_id": 1
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "update": "default_write_concern_coll",
+              "updates": [
+                {
+                  "q": {
+                    "_id": 1
+                  },
+                  "u": {
+                    "$set": {
+                      "x": 1
+                    }
+                  }
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "insert": "default_write_concern_coll",
+              "documents": [
+                {
+                  "_id": 2
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "update": "default_write_concern_coll",
+              "updates": [
+                {
+                  "q": {
+                    "_id": 1
+                  },
+                  "u": {
+                    "x": 2
+                  }
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "insert": "default_write_concern_coll",
+              "documents": [
+                {
+                  "_id": 3
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "update": "default_write_concern_coll",
+              "updates": [
+                {
+                  "q": {
+                    "_id": 1
+                  },
+                  "u": {
+                    "$set": {
+                      "x": 3
+                    }
+                  },
+                  "multi": true
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "delete": "default_write_concern_coll",
+              "deletes": [
+                {
+                  "q": {
+                    "_id": 3
+                  },
+                  "limit": 1
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    },
+    {
+      "description": "InsertOne and InsertMany omit default write concern",
+      "operations": [
+        {
+          "name": "insertOne",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "document": {
+              "_id": 3
+            }
+          }
+        },
+        {
+          "name": "insertMany",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "documents": [
+              {
+                "_id": 4
+              },
+              {
+                "_id": 5
+              }
+            ]
+          }
+        }
+      ],
+      "outcome": {
+        "collection": {
+          "name": "default_write_concern_coll",
+          "data": [
+            {
+              "_id": 1,
+              "x": 11
+            },
+            {
+              "_id": 2,
+              "x": 22
+            },
+            {
+              "_id": 3
+            },
+            {
+              "_id": 4
+            },
+            {
+              "_id": 5
+            }
+          ]
+        }
+      },
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "insert": "default_write_concern_coll",
+              "documents": [
+                {
+                  "_id": 3
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "insert": "default_write_concern_coll",
+              "documents": [
+                {
+                  "_id": 4
+                },
+                {
+                  "_id": 5
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    },
+    {
+      "description": "UpdateOne, UpdateMany, and ReplaceOne omit default write concern",
+      "operations": [
+        {
+          "name": "updateOne",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "filter": {
+              "_id": 1
+            },
+            "update": {
+              "$set": {
+                "x": 1
+              }
+            }
+          }
+        },
+        {
+          "name": "updateMany",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "filter": {
+              "_id": 2
+            },
+            "update": {
+              "$set": {
+                "x": 2
+              }
+            }
+          }
+        },
+        {
+          "name": "replaceOne",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "filter": {
+              "_id": 2
+            },
+            "replacement": {
+              "x": 3
+            }
+          }
+        }
+      ],
+      "outcome": {
+        "collection": {
+          "name": "default_write_concern_coll",
+          "data": [
+            {
+              "_id": 1,
+              "x": 1
+            },
+            {
+              "_id": 2,
+              "x": 3
+            }
+          ]
+        }
+      },
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "update": "default_write_concern_coll",
+              "updates": [
+                {
+                  "q": {
+                    "_id": 1
+                  },
+                  "u": {
+                    "$set": {
+                      "x": 1
+                    }
+                  }
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "update": "default_write_concern_coll",
+              "updates": [
+                {
+                  "q": {
+                    "_id": 2
+                  },
+                  "u": {
+                    "$set": {
+                      "x": 2
+                    }
+                  },
+                  "multi": true
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "update": "default_write_concern_coll",
+              "updates": [
+                {
+                  "q": {
+                    "_id": 2
+                  },
+                  "u": {
+                    "x": 3
+                  }
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    }
+  ]
+}
diff --git a/test/spec/read-write-concern/operation/default-write-concern-2.6.yml b/test/spec/read-write-concern/operation/default-write-concern-2.6.yml
new file mode 100644
index 0000000000..725bcfca12
--- /dev/null
+++ b/test/spec/read-write-concern/operation/default-write-concern-2.6.yml
@@ -0,0 +1,215 @@
+# Test that setting a default write concern does not add a write concern
+# to the command sent over the wire.
+# Test operations that require 2.6+ server.
+
+data:
+  - {_id: 1, x: 11}
+  - {_id: 2, x: 22}
+collection_name: &collection_name default_write_concern_coll
+database_name: &database_name default_write_concern_db
+
+runOn:
+    - minServerVersion: "2.6"
+
+tests:
+  - description: DeleteOne omits default write concern
+    operations:
+      - name: deleteOne
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          filter: {}
+        result:
+          deletedCount: 1
+    expectations:
+      - command_started_event:
+          command:
+            delete: *collection_name
+            deletes:
+              - {q: {}, limit: 1}
+            writeConcern: null
+  - description: DeleteMany omits default write concern
+    operations:
+      - name: deleteMany
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          filter: {}
+        result:
+          deletedCount: 2
+    expectations:
+      - command_started_event:
+          command:
+            delete: *collection_name
+            deletes: [{q: {}, limit: 0}]
+            writeConcern: null
+  - description: BulkWrite with all models omits default write concern
+    operations:
+      - name: bulkWrite
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          ordered: true
+          requests:
+            - name: deleteMany
+              arguments:
+                filter: {}
+            - name: insertOne
+              arguments:
+                document: {_id: 1}
+            - name: updateOne
+              arguments:
+                filter: {_id: 1}
+                update: {$set: {x: 1}}
+            - name: insertOne
+              arguments:
+                document: {_id: 2}
+            - name: replaceOne
+              arguments:
+                filter: {_id: 1}
+                replacement: {x: 2}
+            - name: insertOne
+              arguments:
+                document: {_id: 3}
+            - name: updateMany
+              arguments:
+                filter: {_id: 1}
+                update: {$set: {x: 3}}
+            - name: deleteOne
+              arguments:
+                filter: {_id: 3}
+    outcome:
+      collection:
+        name: *collection_name
+        data:
+          - {_id: 1, x: 3}
+          - {_id: 2}
+    expectations:
+      - command_started_event:
+          command:
+            delete: *collection_name
+            deletes: [{q: {}, limit: 0}]
+            writeConcern: null
+      - command_started_event:
+          command:
+            insert: *collection_name
+            documents:
+              - {_id: 1}
+            writeConcern: null
+      - command_started_event:
+          command:
+            update: *collection_name
+            updates:
+              - {q: {_id: 1}, u: {$set: {x: 1}}}
+            writeConcern: null
+      - command_started_event:
+          command:
+            insert: *collection_name
+            documents:
+              - {_id: 2}
+            writeConcern: null
+      - command_started_event:
+          command:
+            update: *collection_name
+            updates:
+              - {q: {_id: 1}, u: {x: 2}}
+            writeConcern: null
+      - command_started_event:
+          command:
+            insert: *collection_name
+            documents:
+              - {_id: 3}
+            writeConcern: null
+      - command_started_event:
+          command:
+            update: *collection_name
+            updates: 
+              - {q: {_id: 1}, u: {$set: {x: 3}}, multi: true}
+            writeConcern: null
+      - command_started_event:
+          command:
+            delete: *collection_name
+            deletes: [{q: {_id: 3}, limit: 1}]
+            writeConcern: null
+  - description: 'InsertOne and InsertMany omit default write concern'
+    operations:
+      - name: insertOne
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          document: {_id: 3}
+      - name: insertMany
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          documents:
+            - {_id: 4}
+            - {_id: 5}
+    outcome:
+      collection:
+        name: *collection_name
+        data:
+          - {_id: 1, x: 11}
+          - {_id: 2, x: 22}
+          - {_id: 3}
+          - {_id: 4}
+          - {_id: 5}
+    expectations:
+      - command_started_event:
+          command:
+            insert: *collection_name
+            documents:
+              - {_id: 3}
+            writeConcern: null
+      - command_started_event:
+          command:
+            insert: *collection_name
+            documents:
+              - {_id: 4}
+              - {_id: 5}
+            writeConcern: null
+  - description: 'UpdateOne, UpdateMany, and ReplaceOne omit default write concern'
+    operations:
+      - name: updateOne
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          filter: {_id: 1}
+          update: {$set: {x: 1}}
+      - name: updateMany
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          filter: {_id: 2}
+          update: {$set: {x: 2}}
+      - name: replaceOne
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          filter: {_id: 2}
+          replacement: {x: 3}
+    outcome:
+      collection:
+        name: *collection_name
+        data:
+          - {_id: 1, x: 1}
+          - {_id: 2, x: 3}
+    expectations:
+      - command_started_event:
+          command:
+            update: *collection_name
+            updates:
+              - {q: {_id: 1}, u: {$set: {x: 1}}}
+            writeConcern: null
+      - command_started_event:
+          command:
+            update: *collection_name
+            updates:
+              - {q: {_id: 2}, u: {$set: {x: 2}}, multi: true}
+            writeConcern: null
+      - command_started_event:
+          command:
+            update: *collection_name
+            updates:
+              - {q: {_id: 2}, u: {x: 3}}
+            writeConcern: null
\ No newline at end of file
diff --git a/test/spec/read-write-concern/operation/default-write-concern-3.2.json b/test/spec/read-write-concern/operation/default-write-concern-3.2.json
new file mode 100644
index 0000000000..04dd231f04
--- /dev/null
+++ b/test/spec/read-write-concern/operation/default-write-concern-3.2.json
@@ -0,0 +1,125 @@
+{
+  "data": [
+    {
+      "_id": 1,
+      "x": 11
+    },
+    {
+      "_id": 2,
+      "x": 22
+    }
+  ],
+  "collection_name": "default_write_concern_coll",
+  "database_name": "default_write_concern_db",
+  "runOn": [
+    {
+      "minServerVersion": "3.2"
+    }
+  ],
+  "tests": [
+    {
+      "description": "findAndModify operations omit default write concern",
+      "operations": [
+        {
+          "name": "findOneAndUpdate",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "filter": {
+              "_id": 1
+            },
+            "update": {
+              "$set": {
+                "x": 1
+              }
+            }
+          }
+        },
+        {
+          "name": "findOneAndReplace",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "filter": {
+              "_id": 2
+            },
+            "replacement": {
+              "x": 2
+            }
+          }
+        },
+        {
+          "name": "findOneAndDelete",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "filter": {
+              "_id": 2
+            }
+          }
+        }
+      ],
+      "outcome": {
+        "collection": {
+          "name": "default_write_concern_coll",
+          "data": [
+            {
+              "_id": 1,
+              "x": 1
+            }
+          ]
+        }
+      },
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "findAndModify": "default_write_concern_coll",
+              "query": {
+                "_id": 1
+              },
+              "update": {
+                "$set": {
+                  "x": 1
+                }
+              },
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "findAndModify": "default_write_concern_coll",
+              "query": {
+                "_id": 2
+              },
+              "update": {
+                "x": 2
+              },
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "findAndModify": "default_write_concern_coll",
+              "query": {
+                "_id": 2
+              },
+              "remove": true,
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    }
+  ]
+}
diff --git a/test/spec/read-write-concern/operation/default-write-concern-3.2.yml b/test/spec/read-write-concern/operation/default-write-concern-3.2.yml
new file mode 100644
index 0000000000..dccb7e0d07
--- /dev/null
+++ b/test/spec/read-write-concern/operation/default-write-concern-3.2.yml
@@ -0,0 +1,58 @@
+# Test that setting a default write concern does not add a write concern
+# to the command sent over the wire.
+# Test operations that require 3.2+ server, where findAndModify started
+# to accept a write concern.
+
+data:
+  - {_id: 1, x: 11}
+  - {_id: 2, x: 22}
+collection_name: &collection_name default_write_concern_coll
+database_name: &database_name default_write_concern_db
+
+runOn:
+    - minServerVersion: "3.2"
+
+tests:
+  - description: 'findAndModify operations omit default write concern'
+    operations:
+      - name: findOneAndUpdate
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          filter: {_id: 1}
+          update: {$set: {x: 1}}
+      - name: findOneAndReplace
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          filter: {_id: 2}
+          replacement: {x: 2}
+      - name: findOneAndDelete
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          filter: {_id: 2}
+    outcome:
+      collection:
+        name: *collection_name
+        data:
+          - {_id: 1, x: 1}
+    expectations:
+      - command_started_event:
+          command:
+            findAndModify: *collection_name
+            query: {_id: 1}
+            update: {$set: {x: 1}}
+            writeConcern: null
+      - command_started_event:
+          command:
+            findAndModify: *collection_name
+            query: {_id: 2}
+            update: {x: 2}
+            writeConcern: null
+      - command_started_event:
+          command:
+            findAndModify: *collection_name
+            query: {_id: 2}
+            remove: true
+            writeConcern: null
\ No newline at end of file
diff --git a/test/spec/read-write-concern/operation/default-write-concern-3.4.json b/test/spec/read-write-concern/operation/default-write-concern-3.4.json
new file mode 100644
index 0000000000..6519f6f089
--- /dev/null
+++ b/test/spec/read-write-concern/operation/default-write-concern-3.4.json
@@ -0,0 +1,216 @@
+{
+  "data": [
+    {
+      "_id": 1,
+      "x": 11
+    },
+    {
+      "_id": 2,
+      "x": 22
+    }
+  ],
+  "collection_name": "default_write_concern_coll",
+  "database_name": "default_write_concern_db",
+  "runOn": [
+    {
+      "minServerVersion": "3.4"
+    }
+  ],
+  "tests": [
+    {
+      "description": "Aggregate with $out omits default write concern",
+      "operations": [
+        {
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "name": "aggregate",
+          "arguments": {
+            "pipeline": [
+              {
+                "$match": {
+                  "_id": {
+                    "$gt": 1
+                  }
+                }
+              },
+              {
+                "$out": "other_collection_name"
+              }
+            ]
+          }
+        }
+      ],
+      "outcome": {
+        "collection": {
+          "name": "other_collection_name",
+          "data": [
+            {
+              "_id": 2,
+              "x": 22
+            }
+          ]
+        }
+      },
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "aggregate": "default_write_concern_coll",
+              "pipeline": [
+                {
+                  "$match": {
+                    "_id": {
+                      "$gt": 1
+                    }
+                  }
+                },
+                {
+                  "$out": "other_collection_name"
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    },
+    {
+      "description": "RunCommand with a write command omits default write concern (runCommand should never inherit write concern)",
+      "operations": [
+        {
+          "object": "database",
+          "databaseOptions": {
+            "writeConcern": {}
+          },
+          "name": "runCommand",
+          "command_name": "delete",
+          "arguments": {
+            "command": {
+              "delete": "default_write_concern_coll",
+              "deletes": [
+                {
+                  "q": {},
+                  "limit": 1
+                }
+              ]
+            }
+          }
+        }
+      ],
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "delete": "default_write_concern_coll",
+              "deletes": [
+                {
+                  "q": {},
+                  "limit": 1
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    },
+    {
+      "description": "CreateIndex and dropIndex omits default write concern",
+      "operations": [
+        {
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "name": "createIndex",
+          "arguments": {
+            "keys": {
+              "x": 1
+            }
+          }
+        },
+        {
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "name": "dropIndex",
+          "arguments": {
+            "name": "x_1"
+          }
+        }
+      ],
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "createIndexes": "default_write_concern_coll",
+              "indexes": [
+                {
+                  "name": "x_1",
+                  "key": {
+                    "x": 1
+                  }
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        },
+        {
+          "command_started_event": {
+            "command": {
+              "dropIndexes": "default_write_concern_coll",
+              "index": "x_1",
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    },
+    {
+      "description": "MapReduce omits default write concern",
+      "operations": [
+        {
+          "name": "mapReduce",
+          "object": "collection",
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "arguments": {
+            "map": {
+              "$code": "function inc() { return emit(0, this.x + 1) }"
+            },
+            "reduce": {
+              "$code": "function sum(key, values) { return values.reduce((acc, x) => acc + x); }"
+            },
+            "out": {
+              "inline": 1
+            }
+          }
+        }
+      ],
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "mapReduce": "default_write_concern_coll",
+              "map": {
+                "$code": "function inc() { return emit(0, this.x + 1) }"
+              },
+              "reduce": {
+                "$code": "function sum(key, values) { return values.reduce((acc, x) => acc + x); }"
+              },
+              "out": {
+                "inline": 1
+              },
+              "writeConcern": null
+            }
+          }
+        }
+      ]
+    }
+  ]
+}
diff --git a/test/spec/read-write-concern/operation/default-write-concern-3.4.yml b/test/spec/read-write-concern/operation/default-write-concern-3.4.yml
new file mode 100644
index 0000000000..c7b586cadc
--- /dev/null
+++ b/test/spec/read-write-concern/operation/default-write-concern-3.4.yml
@@ -0,0 +1,95 @@
+# Test that setting a default write concern does not add a write concern
+# to the command sent over the wire.
+# Test operations that require 3.4+ server, where all commands started
+# to accept a write concern.
+
+data:
+  - {_id: 1, x: 11}
+  - {_id: 2, x: 22}
+collection_name: &collection_name default_write_concern_coll
+database_name: &database_name default_write_concern_db
+
+runOn:
+    - minServerVersion: "3.4"
+
+tests:
+  - description: Aggregate with $out omits default write concern
+    operations:
+      - object: collection
+        collectionOptions: {writeConcern: {}}
+        name: aggregate
+        arguments:
+          pipeline: &out_pipeline
+            - $match: {_id: {$gt: 1}}
+            - $out: &other_collection_name "other_collection_name"
+    outcome:
+      collection:
+        name: *other_collection_name
+        data:
+          - {_id: 2, x: 22}
+    expectations:
+      - command_started_event:
+          command:
+            aggregate: *collection_name
+            pipeline: *out_pipeline
+            writeConcern: null
+  - description: RunCommand with a write command omits default write concern (runCommand should never inherit write concern)
+    operations:
+      - object: database
+        databaseOptions: {writeConcern: {}}
+        name: runCommand
+        command_name: delete
+        arguments:
+          command:
+            delete: *collection_name
+            deletes:
+              - {q: {}, limit: 1}
+    expectations:
+      - command_started_event:
+          command:
+            delete: *collection_name
+            deletes:
+              - {q: {}, limit: 1}
+            writeConcern: null
+  - description: CreateIndex and dropIndex omits default write concern 
+    operations:
+      - object: collection
+        collectionOptions: {writeConcern: {}}
+        name: createIndex
+        arguments:
+          keys: {x: 1}
+      - object: collection
+        collectionOptions: {writeConcern: {}}
+        name: dropIndex
+        arguments:
+          name: x_1
+    expectations:
+      - command_started_event:
+          command:
+            createIndexes: *collection_name
+            indexes:
+              - name: x_1
+                key: {x: 1}
+            writeConcern: null
+      - command_started_event:
+          command:
+            dropIndexes: *collection_name
+            index: x_1
+            writeConcern: null
+  - description: MapReduce omits default write concern
+    operations:
+      - name: mapReduce
+        object: collection
+        collectionOptions: {writeConcern: {}}
+        arguments:
+          map: { $code: 'function inc() { return emit(0, this.x + 1) }' }
+          reduce: { $code: 'function sum(key, values) { return values.reduce((acc, x) => acc + x); }' }
+          out: { inline: 1 }
+    expectations:
+      - command_started_event:
+          command:
+            mapReduce: *collection_name
+            map: { $code: 'function inc() { return emit(0, this.x + 1) }' }
+            reduce: { $code: 'function sum(key, values) { return values.reduce((acc, x) => acc + x); }' }
+            out: { inline: 1 }
+            writeConcern: null
\ No newline at end of file
diff --git a/test/spec/read-write-concern/operation/default-write-concern-4.2.json b/test/spec/read-write-concern/operation/default-write-concern-4.2.json
new file mode 100644
index 0000000000..fef192d1a3
--- /dev/null
+++ b/test/spec/read-write-concern/operation/default-write-concern-4.2.json
@@ -0,0 +1,87 @@
+{
+  "data": [
+    {
+      "_id": 1,
+      "x": 11
+    },
+    {
+      "_id": 2,
+      "x": 22
+    }
+  ],
+  "collection_name": "default_write_concern_coll",
+  "database_name": "default_write_concern_db",
+  "runOn": [
+    {
+      "minServerVersion": "4.2"
+    }
+  ],
+  "tests": [
+    {
+      "description": "Aggregate with $merge omits default write concern",
+      "operations": [
+        {
+          "object": "collection",
+          "databaseOptions": {
+            "writeConcern": {}
+          },
+          "collectionOptions": {
+            "writeConcern": {}
+          },
+          "name": "aggregate",
+          "arguments": {
+            "pipeline": [
+              {
+                "$match": {
+                  "_id": {
+                    "$gt": 1
+                  }
+                }
+              },
+              {
+                "$merge": {
+                  "into": "other_collection_name"
+                }
+              }
+            ]
+          }
+        }
+      ],
+      "expectations": [
+        {
+          "command_started_event": {
+            "command": {
+              "aggregate": "default_write_concern_coll",
+              "pipeline": [
+                {
+                  "$match": {
+                    "_id": {
+                      "$gt": 1
+                    }
+                  }
+                },
+                {
+                  "$merge": {
+                    "into": "other_collection_name"
+                  }
+                }
+              ],
+              "writeConcern": null
+            }
+          }
+        }
+      ],
+      "outcome": {
+        "collection": {
+          "name": "other_collection_name",
+          "data": [
+            {
+              "_id": 2,
+              "x": 22
+            }
+          ]
+        }
+      }
+    }
+  ]
+}
diff --git a/test/spec/read-write-concern/operation/default-write-concern-4.2.yml b/test/spec/read-write-concern/operation/default-write-concern-4.2.yml
new file mode 100644
index 0000000000..6039b55814
--- /dev/null
+++ b/test/spec/read-write-concern/operation/default-write-concern-4.2.yml
@@ -0,0 +1,36 @@
+# Test that setting a default write concern does not add a write concern
+# to the command sent over the wire.
+# Test operations that require 4.2+ server.
+
+data:
+  - {_id: 1, x: 11}
+  - {_id: 2, x: 22}
+collection_name: &collection_name default_write_concern_coll
+database_name: &database_name default_write_concern_db
+
+runOn:
+    - minServerVersion: "4.2"
+
+tests:
+  - description: Aggregate with $merge omits default write concern
+    operations:
+      - object: collection
+        databaseOptions: {writeConcern: {}}
+        collectionOptions: {writeConcern: {}}
+        name: aggregate
+        arguments:
+          pipeline: &merge_pipeline
+            - $match: {_id: {$gt: 1}}
+            - $merge: {into: &other_collection_name "other_collection_name" }
+    expectations:
+      - command_started_event:
+          command:
+            aggregate: *collection_name
+            pipeline: *merge_pipeline
+            # "null" fields will be checked for non-existence
+            writeConcern: null
+    outcome:
+      collection:
+        name: *other_collection_name
+        data:
+          - {_id: 2, x: 22}
\ No newline at end of file