fix: make it possible to call through to underlying stub in stub inst…

…ance (#2503)

* fix: make it possible to call through to underlying stub in stub instances

refs #2477
refs #2501

* internal: Extract underlying createStubInstance

* internal: extract tests into own module

* internal: extract sinon type checking into own module

closes #2501

lib/sinon/create-stub-instance.js

@@ -0,0 +1,36 @@
+"use strict";
+
+const stub = require("./stub");
+const sinonType = require("./util/core/sinon-type");
+const forEach = require("@sinonjs/commons").prototypes.array.forEach;
+
+function isStub(value) {
+    return sinonType.get(value) === "stub";
+}
+
+module.exports = function createStubInstance(constructor, overrides) {
+    if (typeof constructor !== "function") {
+        throw new TypeError("The constructor should be a function.");
+    }
+
+    const stubInstance = Object.create(constructor.prototype);
+    sinonType.set(stubInstance, "stub-instance");
+
+    const stubbedObject = stub(stubInstance);
+
+    forEach(Object.keys(overrides || {}), function (propertyName) {
+        if (propertyName in stubbedObject) {
+            var value = overrides[propertyName];
+            if (isStub(value)) {
+                stubbedObject[propertyName] = value;
+            } else {
+                stubbedObject[propertyName].returns(value);
+            }
+        } else {
+            throw new Error(
+                `Cannot stub ${propertyName}. Property does not exist!`
+            );
+        }
+    });
+    return stubbedObject;
+};

lib/sinon/sandbox.js

@@ -11,6 +11,7 @@ var sinonClock = require("./util/fake-timers");
 var sinonMock = require("./mock");
 var sinonSpy = require("./spy");
 var sinonStub = require("./stub");
+var sinonCreateStubInstance = require("./create-stub-instance");
 var sinonFake = require("./fake");
 var valueToString = require("@sinonjs/commons").valueToString;
 var fakeServer = require("nise").fakeServer;
@@ -71,7 +72,7 @@ function Sandbox() {
     };
 
     sandbox.createStubInstance = function createStubInstance() {
-        var stubbed = sinonStub.createStubInstance.apply(null, arguments);
+        var stubbed = sinonCreateStubInstance.apply(null, arguments);
 
         var ownMethods = collectOwnMethods(stubbed);
 

lib/sinon/stub.js

@@ -12,6 +12,7 @@ var spy = require("./spy");
 var extend = require("./util/core/extend");
 var getPropertyDescriptor = require("./util/core/get-property-descriptor");
 var isEsModule = require("./util/core/is-es-module");
+var sinonType = require("./util/core/sinon-type");
 var wrapMethod = require("./util/core/wrap-method");
 var throwOnFalsyObject = require("./throw-on-falsy-object");
 var valueToString = require("@sinonjs/commons").valueToString;
@@ -58,6 +59,8 @@ function createStub(originalFunc) {
         id: `stub#${uuid++}`,
     });
 
+    sinonType.set(proxy, "stub");
+
     return proxy;
 }
 
@@ -126,35 +129,6 @@ function stub(object, property) {
     return isStubbingNonFuncProperty ? s : wrapMethod(object, property, s);
 }
 
-stub.createStubInstance = function (constructor, overrides) {
-    if (typeof constructor !== "function") {
-        throw new TypeError("The constructor should be a function.");
-    }
-
-    // eslint-disable-next-line no-empty-function
-    const noop = () => {};
-    const defaultNoOpInstance = Object.create(constructor.prototype);
-    walkObject((obj, prop) => (obj[prop] = noop), defaultNoOpInstance);
-
-    const stubbedObject = stub(defaultNoOpInstance);
-
-    forEach(Object.keys(overrides || {}), function (propertyName) {
-        if (propertyName in stubbedObject) {
-            var value = overrides[propertyName];
-            if (value && value.createStubInstance) {
-                stubbedObject[propertyName] = value;
-            } else {
-                stubbedObject[propertyName].returns(value);
-            }
-        } else {
-            throw new Error(
-                `Cannot stub ${propertyName}. Property does not exist!`
-            );
-        }
-    });
-    return stubbedObject;
-};
-
 function assertValidPropertyDescriptor(descriptor, property) {
     if (!descriptor || !property) {
         return;

lib/sinon/util/core/sinon-type.js

@@ -0,0 +1,22 @@
+"use strict";
+
+const sinonTypeSymbolProperty = Symbol("SinonType");
+
+module.exports = {
+    /**
+     * Set the type of a Sinon object to make it possible to identify it later at runtime
+     *
+     * @param {object|Function} object  object/function to set the type on
+     * @param {string} type the named type of the object/function
+     */
+    set(object, type) {
+        Object.defineProperty(object, sinonTypeSymbolProperty, {
+            value: type,
+            configurable: false,
+            enumerable: false,
+        });
+    },
+    get(object) {
+        return object && object[sinonTypeSymbolProperty];
+    },
+};

lib/sinon/util/core/wrap-method.js

@@ -1,7 +1,10 @@
 "use strict";
 
+// eslint-disable-next-line no-empty-function
+const noop = () => {};
 var getPropertyDescriptor = require("./get-property-descriptor");
 var extend = require("./extend");
+const sinonType = require("./sinon-type");
 var hasOwnProperty =
     require("@sinonjs/commons").prototypes.object.hasOwnProperty;
 var valueToString = require("@sinonjs/commons").valueToString;
@@ -230,6 +233,11 @@ module.exports = function wrapMethod(object, property, method) {
                 }
             }
         }
+        if (sinonType.get(object) === "stub-instance") {
+            // this is simply to avoid errors after restoring if something should
+            // traverse the object in a cleanup phase, ref #2477
+            object[property] = noop;
+        }
     }
 
     return method;

test/create-stub-instance-test.js

@@ -0,0 +1,158 @@
+"use strict";
+
+var referee = require("@sinonjs/referee");
+var createStub = require("../lib/sinon/stub");
+var createStubInstance = require("../lib/sinon/create-stub-instance");
+var assert = referee.assert;
+var refute = referee.refute;
+
+describe("createStubInstance", function () {
+    it("stubs existing methods", function () {
+        var Class = function () {
+            return;
+        };
+        Class.prototype.method = function () {
+            return;
+        };
+
+        var stub = createStubInstance(Class);
+        stub.method.returns(3);
+        assert.equals(3, stub.method());
+    });
+
+    it("throws with no methods to stub", function () {
+        var Class = function () {
+            return;
+        };
+
+        assert.exception(
+            function () {
+                createStubInstance(Class);
+            },
+            {
+                message:
+                    "Found no methods on object to which we could apply mutations",
+            }
+        );
+    });
+
+    it("doesn't call the constructor", function () {
+        var Class = function (a, b) {
+            var c = a + b;
+            throw c;
+        };
+        Class.prototype.method = function () {
+            return;
+        };
+
+        var stub = createStubInstance(Class);
+        refute.exception(function () {
+            stub.method(3);
+        });
+    });
+
+    it("retains non function values", function () {
+        var TYPE = "some-value";
+        var Class = function () {
+            return;
+        };
+        Class.prototype.method = function () {
+            return;
+        };
+        Class.prototype.type = TYPE;
+
+        var stub = createStubInstance(Class);
+        assert.equals(TYPE, stub.type);
+    });
+
+    it("has no side effects on the prototype", function () {
+        var proto = {
+            method: function () {
+                throw new Error("error");
+            },
+        };
+        var Class = function () {
+            return;
+        };
+        Class.prototype = proto;
+
+        var stub = createStubInstance(Class);
+        refute.exception(stub.method);
+        assert.exception(proto.method);
+    });
+
+    it("throws exception for non function params", function () {
+        var types = [{}, 3, "hi!"];
+
+        for (var i = 0; i < types.length; i++) {
+            // yes, it's silly to create functions in a loop, it's also a test
+            // eslint-disable-next-line no-loop-func
+            assert.exception(function () {
+                createStubInstance(types[i]);
+            });
+        }
+    });
+
+    it("allows providing optional overrides", function () {
+        var Class = function () {
+            return;
+        };
+        Class.prototype.method = function () {
+            return;
+        };
+
+        var stub = createStubInstance(Class, {
+            method: createStub().returns(3),
+        });
+
+        assert.equals(3, stub.method());
+    });
+
+    it("allows providing optional returned values", function () {
+        var Class = function () {
+            return;
+        };
+        Class.prototype.method = function () {
+            return;
+        };
+
+        var stub = createStubInstance(Class, {
+            method: 3,
+        });
+
+        assert.equals(3, stub.method());
+    });
+
+    it("allows providing null as a return value", function () {
+        var Class = function () {
+            return;
+        };
+        Class.prototype.method = function () {
+            return;
+        };
+
+        var stub = createStubInstance(Class, {
+            method: null,
+        });
+
+        assert.equals(null, stub.method());
+    });
+
+    it("throws an exception when trying to override non-existing property", function () {
+        var Class = function () {
+            return;
+        };
+        Class.prototype.method = function () {
+            return;
+        };
+
+        assert.exception(
+            function () {
+                createStubInstance(Class, {
+                    foo: createStub().returns(3),
+                });
+            },
+            { message: "Cannot stub foo. Property does not exist!" }
+        );
+    });
+});

test/issues/issues-test.js

@@ -805,4 +805,21 @@ describe("issues", function () {
             assert.isUndefined(restoredPropertyDescriptor);
         });
     });
+
+    describe("#2501 - createStubInstance stubs are not able to call through to the underlying function on the prototype", function () {
+        it("should be able call through to the underlying function on the prototype", function () {
+            class Foo {
+                testMethod() {
+                    this.wasCalled = true;
+                    return 42;
+                }
+            }
+
+            const fooStubInstance = this.sandbox.createStubInstance(Foo);
+            fooStubInstance.testMethod.callThrough();
+            // const fooStubInstance = new Foo()
+            fooStubInstance.testMethod();
+            // assert.isTrue(fooStubInstance.wasCalled);
+        });
+    });
 });