From c3155665c19b5106991cd708137d7d8272e5d13f Mon Sep 17 00:00:00 2001
From: Sina Mahmoodi <1591639+s1na@users.noreply.github.com>
Date: Tue, 22 Jan 2019 14:17:12 +0100
Subject: [PATCH] Extract db-related methods from baseTrie (#74)

* Mv raw methods to DB class
* Add ScratchDB which CheckpointTrie uses
* Rename checkpoint-trie to checkpointTrie
* Add comments to scratch
* Fix linting errors
* Regenerate docs
* Rm raw methods and their tests
* Rename DB._db to DB._leveldb
* Make createScratchReadStream private
* Fix linting error and jsdoc comments
* Regenerate docs
* Add tests for db, scratch and more cases for checkpoint
* Fix checkpoint copy, add tests for checkpoint and secure copy

Signed-off-by: Sina Mahmoodi <itz.s1na@gmail.com>
---
 docs/index.md                                 | 338 +++++++++++-------
 src/baseTrie.js                               | 104 +-----
 src/{checkpoint-trie.js => checkpointTrie.js} |  88 ++---
 src/db.js                                     |  83 +++++
 src/index.js                                  |   2 +-
 src/scratch.js                                |  42 +++
 src/secure.js                                 |   5 +-
 test/checkpoint.js                            | 128 +++++++
 test/db.js                                    |  55 +++
 test/index.js                                 |  68 ----
 test/rawOPs.js                                |  71 ----
 test/scratch.js                               |  57 +++
 test/secure.js                                |  28 +-
 test/streams.js                               |   2 +-
 14 files changed, 654 insertions(+), 417 deletions(-)
 rename src/{checkpoint-trie.js => checkpointTrie.js} (70%)
 create mode 100644 src/db.js
 create mode 100644 src/scratch.js
 create mode 100644 test/checkpoint.js
 create mode 100644 test/db.js
 delete mode 100644 test/rawOPs.js
 create mode 100644 test/scratch.js

diff --git a/docs/index.md b/docs/index.md
index 1ef081a..0f8e75d 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -2,7 +2,7 @@
 
 ## SecureTrie
 
-[src/secure.js:12-43][1]
+[src/secure.js:12-44][1]
 
 **Extends Trie**
 
@@ -12,100 +12,68 @@ It has the same methods and constructor as `Trie`.
 
 ## Trie
 
-[src/baseTrie.js:23-779][2]
+[src/baseTrie.js:25-701][2]
 
-Use `require('merkel-patricia-tree')` for the base interface. In Ethereum applications stick with the Secure Trie Overlay `require('merkel-patricia-tree/secure')`. The API for the raw and the secure interface are about the same
+Use `require('merkel-patricia-tree')` for the base interface. In Ethereum applications
+stick with the Secure Trie Overlay `require('merkel-patricia-tree/secure')`.
+The API for the raw and the secure interface are about the same
 
 ### Parameters
 
--   `db` **[Object][3]?** An instance of [levelup][4] or a compatible API. If the db is `null` or left undefined, then the trie will be stored in memory via [memdown][5]
--   `root` **([Buffer][6] \| [String][7])?** A hex `String` or `Buffer` for the root of a previously stored trie
+-   `db` **[Object][3]?** An instance of `DB`.
+    If the db is `null` or left undefined, then the trie will be stored in memory via [memdown][4]
+-   `root` **([Buffer][5] \| [String][6])?** A hex `String` or `Buffer` for the root of a previously stored trie
 
 ### Properties
 
--   `root` **[Buffer][6]** The current root of the `trie`
--   `isCheckpoint` **[Boolean][8]** determines if you are saving to a checkpoint or directly to the db
--   `EMPTY_TRIE_ROOT` **[Buffer][6]** the Root for an empty trie
+-   `root` **[Buffer][5]** The current root of the `trie`
+-   `EMPTY_TRIE_ROOT` **[Buffer][5]** the Root for an empty trie
 
 ### get
 
-[src/baseTrie.js:63-75][9]
+[src/baseTrie.js:59-71][7]
 
 Gets a value given a `key`
 
 #### Parameters
 
--   `key` **([Buffer][6] \| [String][7])** the key to search for
--   `cb` **[Function][10]** A callback `Function` which is given the arguments `err` - for errors that may have occured and `value` - the found value in a `Buffer` or if no value was found `null`
+-   `key` **([Buffer][5] \| [String][6])** the key to search for
+-   `cb` **[Function][8]** A callback `Function` which is given the arguments `err` - for errors that may have occured and `value` - the found value in a `Buffer` or if no value was found `null`
 
 ### put
 
-[src/baseTrie.js:85-109][11]
+[src/baseTrie.js:81-105][9]
 
 Stores a given `value` at the given `key`
 
 #### Parameters
 
--   `key` **([Buffer][6] \| [String][7])** 
--   `Value` **([Buffer][6] \| [String][7])** 
--   `cb` **[Function][10]** A callback `Function` which is given the argument `err` - for errors that may have occured
+-   `key` **([Buffer][5] \| [String][6])** 
+-   `Value` **([Buffer][5] \| [String][6])** 
+-   `cb` **[Function][8]** A callback `Function` which is given the argument `err` - for errors that may have occured
 
 ### del
 
-[src/baseTrie.js:118-134][12]
+[src/baseTrie.js:114-130][10]
 
 deletes a value given a `key`
 
 #### Parameters
 
--   `key` **([Buffer][6] \| [String][7])** 
--   `callback` **[Function][10]** the callback `Function`
-
-### getRaw
-
-[src/baseTrie.js:143-160][13]
-
-Retrieves a raw value in the underlying db
-
-#### Parameters
-
--   `key` **[Buffer][6]** 
--   `callback` **[Function][10]** A callback `Function`, which is given the arguments `err` - for errors that may have occured and `value` - the found value in a `Buffer` or if no value was found `null`.
-
-### putRaw
-
-[src/baseTrie.js:190-199][14]
-
-Writes a value directly to the underlining db
-
-#### Parameters
-
--   `key` **([Buffer][6] \| [String][7])** The key as a `Buffer` or `String`
--   `value` **[Buffer][6]** The value to be stored
--   `callback` **[Function][10]** A callback `Function`, which is given the argument `err` - for errors that may have occured
-
-### delRaw
-
-[src/baseTrie.js:208-216][15]
-
-Removes a raw value in the underlying db
-
-#### Parameters
-
--   `key` **([Buffer][6] \| [String][7])** 
--   `callback` **[Function][10]** A callback `Function`, which is given the argument `err` - for errors that may have occured
+-   `key` **([Buffer][5] \| [String][6])** 
+-   `callback` **[Function][8]** the callback `Function`
 
 ### findPath
 
-[src/baseTrie.js:250-296][16]
+[src/baseTrie.js:171-217][11]
 
 Tries to find a path to the node for the given key
 It returns a `stack` of nodes to the closet node
 
 #### Parameters
 
--   `null-null` **([String][7] \| [Buffer][6])** key - the search key
--   `null-null` **[Function][10]** cb - the callback function. Its is given the following
+-   `null-null` **([String][6] \| [Buffer][5])** key - the search key
+-   `null-null` **[Function][8]** cb - the callback function. Its is given the following
     arguments-   err - any errors encontered
     -   node - the last node found
     -   keyRemainder - the remaining key nibbles not accounted for
@@ -113,22 +81,22 @@ It returns a `stack` of nodes to the closet node
 
 ### createReadStream
 
-[src/baseTrie.js:728-730][17]
+[src/baseTrie.js:649-651][12]
 
 The `data` event is given an `Object` hat has two properties; the `key` and the `value`. Both should be Buffers.
 
-Returns **[stream.Readable][18]** Returns a [stream][19] of the contents of the `trie`
+Returns **[stream.Readable][13]** Returns a [stream][14] of the contents of the `trie`
 
 ### batch
 
-[src/baseTrie.js:754-764][20]
+[src/baseTrie.js:676-686][15]
 
 The given hash of operations (key additions or deletions) are executed on the DB
 
 #### Parameters
 
--   `ops` **[Array][21]** 
--   `cb` **[Function][10]** 
+-   `ops` **[Array][16]** 
+-   `cb` **[Function][8]** 
 
 #### Examples
 
@@ -145,14 +113,14 @@ trie.batch(ops)
 
 ### checkRoot
 
-[src/baseTrie.js:773-778][22]
+[src/baseTrie.js:695-700][17]
 
 Checks if a given root exists
 
 #### Parameters
 
--   `root` **[Buffer][6]** 
--   `cb` **[Function][10]** 
+-   `root` **[Buffer][5]** 
+-   `cb` **[Function][8]** 
 
 ## Merkle Proof
 
@@ -161,28 +129,28 @@ Static functions for creating/verifying a merkle proof.
 
 ### prove
 
-[src/proof.js:12-29][23]
+[src/proof.js:12-29][18]
 
 Returns a merkle proof for a given key
 
 #### Parameters
 
--   `trie` **[Trie][24]** 
--   `key` **[String][7]** 
--   `cb` **[Function][10]** A callback `Function` (arguments {Error} `err`, {Array.<TrieNode>} `proof`)
+-   `trie` **[Trie][19]** 
+-   `key` **[String][6]** 
+-   `cb` **[Function][8]** A callback `Function` (arguments {Error} `err`, {Array.<TrieNode>} `proof`)
 
 ### verifyProof
 
-[src/proof.js:39-100][25]
+[src/proof.js:39-100][20]
 
 Verifies a merkle proof for a given key
 
 #### Parameters
 
--   `rootHash` **[Buffer][6]** 
--   `key` **[String][7]** 
--   `proof` **[Array][21]&lt;TrieNode>** 
--   `cb` **[Function][10]** A callback `Function` (arguments {Error} `err`, {String} `val`)
+-   `rootHash` **[Buffer][5]** 
+-   `key` **[String][6]** 
+-   `proof` **[Array][16]&lt;TrieNode>** 
+-   `cb` **[Function][8]** A callback `Function` (arguments {Error} `err`, {String} `val`)
 
 ## Internal Util Functions
 
@@ -191,20 +159,20 @@ These are not exposed.
 
 ### addHexPrefix
 
-[src/util/hex.js:7-22][26]
+[src/util/hex.js:7-22][21]
 
 Prepends hex prefix to an array of nibbles.
 
 #### Parameters
 
--   `Array` **[Array][21]** of nibbles
+-   `Array` **[Array][16]** of nibbles
 
-Returns **[Array][21]** returns buffer of encoded data
+Returns **[Array][16]** returns buffer of encoded data
 \*
 
 ### asyncFirstSeries
 
-[src/util/async.js:38-54][27]
+[src/util/async.js:38-54][22]
 
 Take a collection of async fns, call the cb on the first to return a truthy value.
 If all run without a truthy result, return undefined
@@ -217,31 +185,138 @@ If all run without a truthy result, return undefined
 
 ### doKeysMatch
 
-[src/util/nibbles.js:56-59][28]
+[src/util/nibbles.js:56-59][23]
 
 Compare two nibble array keys.
 
 #### Parameters
 
--   `keyA` **[Array][21]** 
--   `keyB` **[Array][21]** 
+-   `keyA` **[Array][16]** 
+-   `keyB` **[Array][16]** 
 
 ## 
 
-[src/util/async.js:3-6][29]
+[src/util/async.js:3-6][24]
 
 Take two or more functions and returns a function  that will execute all of
 the given functions
 
+## 
+
+[src/db.js:3-3][25]
+
+DB is a thin wrapper around the underlying levelup db,
+which validates inputs and sets encoding type.
+
+## 
+
+[src/scratch.js:4-4][26]
+
+An in-memory wrap over `DB` with an upstream DB
+which will be queried when a key is not found
+in the in-memory scratch. This class is used to implement
+checkpointing functionality in CheckpointTrie.
+
+## decodeNode
+
+[src/node/index.js:12-31][27]
+
+Returns node instance given encoded RLP value.
+
+### Parameters
+
+-   `v`  
+
+## constructor
+
+[src/db.js:15-17][28]
+
+Initialize a DB instance. If `leveldb` is not provided, DB
+defaults to an [in-memory store][4].
+
+### Parameters
+
+-   `leveldb` **[Object][3]?** An abstract-leveldown compliant store
+
+## get
+
+[src/db.js:26-36][29]
+
+Retrieves a raw value from leveldb.
+
+### Parameters
+
+-   `key` **[Buffer][5]** 
+-   `cb` **[Function][8]** A callback `Function`, which is given the arguments
+    `err` - for errors that may have occured
+    and `value` - the found value in a `Buffer` or if no value was found `null`.
+
+## put
+
+[src/db.js:45-50][30]
+
+Writes a value directly to leveldb.
+
+### Parameters
+
+-   `key` **[Buffer][5]** The key as a `Buffer` or `String`
+-   `val`  
+-   `cb` **[Function][8]** A callback `Function`, which is given the argument
+    `err` - for errors that may have occured
+-   `value` **[Buffer][5]** The value to be stored
+
+## del
+
+[src/db.js:58-62][31]
+
+Removes a raw value in the underlying leveldb.
+
+### Parameters
+
+-   `key` **[Buffer][5]** 
+-   `cb` **[Function][8]** A callback `Function`, which is given the argument
+    `err` - for errors that may have occured
+
+## batch
+
+[src/db.js:70-74][32]
+
+Performs a batch operation on db.
+
+### Parameters
+
+-   `opStack` **[Array][16]** A stack of levelup operations
+-   `cb` **[Function][8]** A callback `Function`, which is given the argument
+    `err` - for errors that may have occured
+
+## copy
+
+[src/db.js:80-82][33]
+
+Returns a copy of the DB instance, with a reference
+to the **same** underlying leveldb instance.
+
+## get
+
+[src/scratch.js:22-35][34]
+
+Similar to `DB.get`, but first searches in-memory
+scratch DB, if key not found, searches upstream DB.
+
+### Parameters
+
+-   `key`  
+-   `cb`  
+
 ## isCheckpoint
 
-[src/checkpoint-trie.js:27-29][30]
+[src/checkpointTrie.js:31-33][35]
 
 Is the trie during a checkpoint phase?
 
 ## put
 
-[src/secure.js:30-37][31]
+[src/secure.js:31-38][36]
 
 For a falsey value, use the original key
 to avoid double hashing the key.
@@ -254,7 +329,7 @@ to avoid double hashing the key.
 
 ## checkpoint
 
-[src/checkpoint-trie.js:38-46][32]
+[src/checkpointTrie.js:42-50][37]
 
 Creates a checkpoint that can later be reverted to or committed.
 After this is called, no changes to the trie will be permanently saved
@@ -263,111 +338,114 @@ mechanism and would directly write to db.
 
 ## commit
 
-[src/checkpoint-trie.js:55-70][33]
+[src/checkpointTrie.js:59-74][38]
 
 Commits a checkpoint to disk, if current checkpoint is not nested. If
 nested, only sets the parent checkpoint as current checkpoint.
 
 ### Parameters
 
--   `cb` **[Function][10]** the callback
+-   `cb` **[Function][8]** the callback
 
 
 -   Throws **any** If not during a checkpoint phase
 
 ## revert
 
-[src/checkpoint-trie.js:78-92][34]
+[src/checkpointTrie.js:83-97][39]
 
 Reverts the trie to the state it was at when `checkpoint` was first called.
-If during a nested checkpoint, only sets parent as current checkpoint.
+If during a nested checkpoint, sets root to most recent checkpoint, and sets
+parent checkpoint as current.
 
 ### Parameters
 
--   `cb` **[Function][10]** the callback
+-   `cb` **[Function][8]** the callback
 
 ## copy
 
-[src/checkpoint-trie.js:99-104][35]
+[src/checkpointTrie.js:105-114][40]
 
 Returns a copy of the underlying trie with the interface
-of CheckpointTrie.
+of CheckpointTrie. If during a checkpoint, the copy will
+contain the checkpointing metadata (incl. reference to the same scratch).
+
+[1]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/secure.js#L12-L44 "Source code on GitHub"
 
-## createScratchReadStream
+[2]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/baseTrie.js#L25-L701 "Source code on GitHub"
 
-[src/checkpoint-trie.js:111-118][36]
+[3]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
 
-Returns a `ScratchReadStream` based on the state updates
-since checkpoint.
+[4]: https://github.com/Level/memdown
 
-[1]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/secure.js#L12-L43 "Source code on GitHub"
+[5]: https://nodejs.org/api/buffer.html
 
-[2]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L23-L779 "Source code on GitHub"
+[6]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String
 
-[3]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
+[7]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/baseTrie.js#L59-L71 "Source code on GitHub"
 
-[4]: https://github.com/rvagg/node-levelup/
+[8]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function
 
-[5]: https://github.com/rvagg/memdown
+[9]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/baseTrie.js#L81-L105 "Source code on GitHub"
 
-[6]: https://nodejs.org/api/buffer.html
+[10]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/baseTrie.js#L114-L130 "Source code on GitHub"
 
-[7]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String
+[11]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/baseTrie.js#L171-L217 "Source code on GitHub"
 
-[8]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean
+[12]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/baseTrie.js#L649-L651 "Source code on GitHub"
 
-[9]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L63-L75 "Source code on GitHub"
+[13]: https://nodejs.org/api/stream.html#stream_class_stream_readable
 
-[10]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function
+[14]: https://nodejs.org/dist/latest-v5.x/docs/api/stream.html#stream_class_stream_readable
 
-[11]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L85-L109 "Source code on GitHub"
+[15]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/baseTrie.js#L676-L686 "Source code on GitHub"
 
-[12]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L118-L134 "Source code on GitHub"
+[16]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array
 
-[13]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L143-L160 "Source code on GitHub"
+[17]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/baseTrie.js#L695-L700 "Source code on GitHub"
 
-[14]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L190-L199 "Source code on GitHub"
+[18]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/proof.js#L12-L29 "Source code on GitHub"
 
-[15]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L208-L216 "Source code on GitHub"
+[19]: #trie
 
-[16]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L250-L296 "Source code on GitHub"
+[20]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/proof.js#L39-L100 "Source code on GitHub"
 
-[17]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L728-L730 "Source code on GitHub"
+[21]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/util/hex.js#L7-L22 "Source code on GitHub"
 
-[18]: https://nodejs.org/api/stream.html#stream_class_stream_readable
+[22]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/util/async.js#L38-L54 "Source code on GitHub"
 
-[19]: https://nodejs.org/dist/latest-v5.x/docs/api/stream.html#stream_class_stream_readable
+[23]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/util/nibbles.js#L56-L59 "Source code on GitHub"
 
-[20]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L754-L764 "Source code on GitHub"
+[24]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/util/async.js#L3-L6 "Source code on GitHub"
 
-[21]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array
+[25]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/db.js#L3-L3 "Source code on GitHub"
 
-[22]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/baseTrie.js#L773-L778 "Source code on GitHub"
+[26]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/scratch.js#L4-L4 "Source code on GitHub"
 
-[23]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/proof.js#L12-L29 "Source code on GitHub"
+[27]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/node/index.js#L12-L31 "Source code on GitHub"
 
-[24]: #trie
+[28]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/db.js#L15-L17 "Source code on GitHub"
 
-[25]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/proof.js#L39-L100 "Source code on GitHub"
+[29]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/db.js#L26-L36 "Source code on GitHub"
 
-[26]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/util/hex.js#L7-L22 "Source code on GitHub"
+[30]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/db.js#L45-L50 "Source code on GitHub"
 
-[27]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/util/async.js#L38-L54 "Source code on GitHub"
+[31]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/db.js#L58-L62 "Source code on GitHub"
 
-[28]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/util/nibbles.js#L56-L59 "Source code on GitHub"
+[32]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/db.js#L70-L74 "Source code on GitHub"
 
-[29]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/util/async.js#L3-L6 "Source code on GitHub"
+[33]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/db.js#L80-L82 "Source code on GitHub"
 
-[30]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/checkpoint-trie.js#L27-L29 "Source code on GitHub"
+[34]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/scratch.js#L22-L35 "Source code on GitHub"
 
-[31]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/secure.js#L30-L37 "Source code on GitHub"
+[35]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/checkpointTrie.js#L31-L33 "Source code on GitHub"
 
-[32]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/checkpoint-trie.js#L38-L46 "Source code on GitHub"
+[36]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/secure.js#L31-L38 "Source code on GitHub"
 
-[33]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/checkpoint-trie.js#L55-L70 "Source code on GitHub"
+[37]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/checkpointTrie.js#L42-L50 "Source code on GitHub"
 
-[34]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/checkpoint-trie.js#L78-L92 "Source code on GitHub"
+[38]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/checkpointTrie.js#L59-L74 "Source code on GitHub"
 
-[35]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/checkpoint-trie.js#L99-L104 "Source code on GitHub"
+[39]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/checkpointTrie.js#L83-L97 "Source code on GitHub"
 
-[36]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/4194fd7855a3b9bd85742ea3c20ebfc405182742/src/checkpoint-trie.js#L111-L118 "Source code on GitHub"
+[40]: https://git@github.com/:ethereumjs/merkle-patricia-tree/blob/a4c7f5423da6a9d23ff0aa886c2fd560dac05b7d/src/checkpointTrie.js#L105-L114 "Source code on GitHub"
diff --git a/src/baseTrie.js b/src/baseTrie.js
index d668e7f..b7a3796 100644
--- a/src/baseTrie.js
+++ b/src/baseTrie.js
@@ -1,23 +1,25 @@
 const assert = require('assert')
-const level = require('level-mem')
 const async = require('async')
 const rlp = require('rlp')
 const ethUtil = require('ethereumjs-util')
 const semaphore = require('semaphore')
+const DB = require('./db')
 const TrieNode = require('./trieNode')
 const ReadStream = require('./readStream')
 const PrioritizedTaskExecutor = require('./prioritizedTaskExecutor')
-const { callTogether, asyncFirstSeries } = require('./util/async')
+const { callTogether } = require('./util/async')
 const { stringToNibbles, matchingNibbleLength, doKeysMatch } = require('./util/nibbles')
 
 /**
- * Use `require('merkel-patricia-tree')` for the base interface. In Ethereum applications stick with the Secure Trie Overlay `require('merkel-patricia-tree/secure')`. The API for the raw and the secure interface are about the same
+ * Use `require('merkel-patricia-tree')` for the base interface. In Ethereum applications
+ * stick with the Secure Trie Overlay `require('merkel-patricia-tree/secure')`.
+ * The API for the raw and the secure interface are about the same
  * @class Trie
  * @public
- * @param {Object} [db] An instance of [levelup](https://github.com/rvagg/node-levelup/) or a compatible API. If the db is `null` or left undefined, then the trie will be stored in memory via [memdown](https://github.com/rvagg/memdown)
+ * @param {Object} [db] An instance of `DB`.
+ * If the db is `null` or left undefined, then the trie will be stored in memory via [memdown](https://github.com/Level/memdown)
  * @param {Buffer|String} [root] A hex `String` or `Buffer` for the root of a previously stored trie
  * @prop {Buffer} root The current root of the `trie`
- * @prop {Boolean} isCheckpoint  determines if you are saving to a checkpoint or directly to the db
  * @prop {Buffer} EMPTY_TRIE_ROOT the Root for an empty trie
  */
 module.exports = class Trie {
@@ -26,11 +28,7 @@ module.exports = class Trie {
     this.EMPTY_TRIE_ROOT = ethUtil.SHA3_RLP
     this.sem = semaphore(1)
 
-    // setup dbs
-    this.db = db || level()
-
-    this._getDBs = [this.db]
-    this._putDBs = [this.db]
+    this.db = db || new DB()
 
     Object.defineProperty(this, 'root', {
       set(value) {
@@ -49,8 +47,6 @@ module.exports = class Trie {
     })
 
     this.root = root
-
-    this.putRaw = this._putRaw
   }
 
   /**
@@ -133,38 +129,12 @@ module.exports = class Trie {
     })
   }
 
-  /**
-   * Retrieves a raw value in the underlying db
-   * @method getRaw
-   * @memberof Trie
-   * @param {Buffer} key
-   * @param {Function} callback A callback `Function`, which is given the arguments `err` - for errors that may have occured and `value` - the found value in a `Buffer` or if no value was found `null`.
-   */
-  getRaw (key, cb) {
-    key = ethUtil.toBuffer(key)
-
-    function dbGet (db, cb2) {
-      db.get(key, {
-        keyEncoding: 'binary',
-        valueEncoding: 'binary'
-      }, (err, foundNode) => {
-        if (err || !foundNode) {
-          cb2(null, null)
-        } else {
-          cb2(null, foundNode)
-        }
-      })
-    }
-
-    asyncFirstSeries(this._getDBs, dbGet, cb)
-  }
-
   // retrieves a node from dbs by hash
   _lookupNode (node, cb) {
     if (TrieNode.isRawNode(node)) {
       cb(new TrieNode(node))
     } else {
-      this.getRaw(node, (err, value) => {
+      this.db.get(node, (err, value) => {
         if (err) {
           throw err
         }
@@ -178,60 +148,11 @@ module.exports = class Trie {
     }
   }
 
-  /**
-   * Writes a value directly to the underlining db
-   * @method putRaw
-   * @memberof Trie
-   * @param {Buffer|String} key The key as a `Buffer` or `String`
-   * @param {Buffer} value The value to be stored
-   * @param {Function} callback A callback `Function`, which is given the argument `err` - for errors that may have occured
-   */
-  // TODO: remove the proxy method when changing the caching
-  _putRaw (key, val, cb) {
-    function dbPut (db, cb2) {
-      db.put(key, val, {
-        keyEncoding: 'binary',
-        valueEncoding: 'binary'
-      }, cb2)
-    }
-
-    async.each(this._putDBs, dbPut, cb)
-  }
-
-  /**
-   * Removes a raw value in the underlying db
-   * @method delRaw
-   * @memberof Trie
-   * @param {Buffer|String} key
-   * @param {Function} callback A callback `Function`, which is given the argument `err` - for errors that may have occured
-   */
-  delRaw (key, cb) {
-    function del (db, cb2) {
-      db.del(key, {
-        keyEncoding: 'binary'
-      }, cb2)
-    }
-
-    async.each(this._putDBs, del, cb)
-  }
-
   // writes a single node to dbs
   _putNode (node, cb) {
     const hash = node.hash()
     const serialized = node.serialize()
-    this._putRaw(hash, serialized, cb)
-  }
-
-  // writes many nodes to db
-  _batchNodes (opStack, cb) {
-    function dbBatch (db, cb) {
-      db.batch(opStack, {
-        keyEncoding: 'binary',
-        valueEncoding: 'binary'
-      }, cb)
-    }
-
-    async.each(this._putDBs, dbBatch, cb)
+    this.db.put(hash, serialized, cb)
   }
 
   /**
@@ -560,7 +481,7 @@ module.exports = class Trie {
       this.root = lastRoot
     }
 
-    this._batchNodes(opStack, cb)
+    this.db.batch(opStack, cb)
   }
 
   _deleteNode (key, stack, cb) {
@@ -732,7 +653,8 @@ module.exports = class Trie {
   // creates a new trie backed by the same db
   // and starting at the same root
   copy () {
-    return new Trie(this.db, this.root)
+    const db = this.db.copy()
+    return new Trie(db, this.root)
   }
 
   /**
diff --git a/src/checkpoint-trie.js b/src/checkpointTrie.js
similarity index 70%
rename from src/checkpoint-trie.js
rename to src/checkpointTrie.js
index 5beb3b1..f9998b1 100644
--- a/src/checkpoint-trie.js
+++ b/src/checkpointTrie.js
@@ -1,15 +1,19 @@
 const async = require('async')
-const level = require('level-mem')
 const WriteStream = require('level-ws')
 const BaseTrie = require('./baseTrie')
 const proof = require('./proof.js')
 const ScratchReadStream = require('./scratchReadStream')
+const ScratchDB = require('./scratch')
 const { callTogether } = require('./util/async')
 
 module.exports = class CheckpointTrie extends BaseTrie {
   constructor (...args) {
     super(...args)
+    // Reference to main DB instance
+    this._mainDB = this.db
+    // DB instance used for checkpoints
     this._scratch = null
+    // Roots of trie at the moment of checkpoint
     this._checkpoints = []
   }
 
@@ -71,7 +75,8 @@ module.exports = class CheckpointTrie extends BaseTrie {
 
   /**
    * Reverts the trie to the state it was at when `checkpoint` was first called.
-   * If during a nested checkpoint, only sets parent as current checkpoint.
+   * If during a nested checkpoint, sets root to most recent checkpoint, and sets
+   * parent checkpoint as current.
    * @method revert
    * @param {Function} cb the callback
    */
@@ -93,42 +98,19 @@ module.exports = class CheckpointTrie extends BaseTrie {
 
   /**
    * Returns a copy of the underlying trie with the interface
-   * of CheckpointTrie.
+   * of CheckpointTrie. If during a checkpoint, the copy will
+   * contain the checkpointing metadata (incl. reference to the same scratch).
    * @method copy
    */
   copy () {
-    const trie = new CheckpointTrie(this.db, this.root)
-    trie._scratch = this._scratch
-    // trie._checkpoints = this._checkpoints.slice()
-    return trie
-  }
-
-  /**
-   * Returns a `ScratchReadStream` based on the state updates
-   * since checkpoint.
-   * @method createScratchReadStream
-   */
-  createScratchReadStream (scratch) {
-    const trie = this.copy()
-    scratch = scratch || this._scratch
-    // Only read from the scratch
-    trie._getDBs = [scratch]
-    trie._scratch = scratch
-    return new ScratchReadStream(trie)
-  }
-
-  /**
-   * Puts kv-pair directly to db, ignoring checkpoints.
-   * @private
-   */
-  _overridePutRaw (key, val, cb) {
-    const dbPut = (db, cb2) => {
-      db.put(key, val, {
-        keyEncoding: 'binary',
-        valueEncoding: 'binary'
-      }, cb2)
+    const db = this._mainDB.copy()
+    const trie = new CheckpointTrie(db, this.root)
+    if (this.isCheckpoint) {
+      trie._checkpoints = this._checkpoints.slice()
+      trie._scratch = this._scratch.copy()
+      trie.db = trie._scratch
     }
-    async.each(this.__putDBs, dbPut, cb)
+    return trie
   }
 
   /**
@@ -136,12 +118,8 @@ module.exports = class CheckpointTrie extends BaseTrie {
    * @private
    */
   _enterCpMode () {
-    this._scratch = level()
-    this._getDBs = [this._scratch].concat(this._getDBs)
-    this.__putDBs = this._putDBs
-    this._putDBs = [this._scratch]
-    this._putRaw = this.putRaw
-    this.putRaw = this._overridePutRaw
+    this._scratch = new ScratchDB(this._mainDB)
+    this.db = this._scratch
   }
 
   /**
@@ -149,22 +127,28 @@ module.exports = class CheckpointTrie extends BaseTrie {
    * @private
    */
   _exitCpMode (commitState, cb) {
-    var scratch = this._scratch
+    const scratch = this._scratch
     this._scratch = null
-    this._getDBs = this._getDBs.slice(1)
-    this._putDBs = this.__putDBs
-    this.putRaw = this._putRaw
-
-    const flushScratch = (db, cb) => {
-      this.createScratchReadStream(scratch)
-        .pipe(WriteStream(db))
-        .on('close', cb)
-    }
+    this.db = this._mainDB
 
     if (commitState) {
-      async.map(this._putDBs, flushScratch, cb)
+      this._createScratchReadStream(scratch)
+        .pipe(WriteStream(this.db))
+        .on('close', cb)
     } else {
-      cb()
+      async.nextTick(cb)
     }
   }
+
+  /**
+   * Returns a `ScratchReadStream` based on the state updates
+   * since checkpoint.
+   * @method createScratchReadStream
+   * @private
+   */
+  _createScratchReadStream (scratch) {
+    scratch = scratch || this._scratch
+    const trie = new BaseTrie(scratch, this.root)
+    return new ScratchReadStream(trie)
+  }
 }
diff --git a/src/db.js b/src/db.js
new file mode 100644
index 0000000..f51ab5d
--- /dev/null
+++ b/src/db.js
@@ -0,0 +1,83 @@
+const level = require('level-mem')
+
+const ENCODING_OPTS = { keyEncoding: 'binary', valueEncoding: 'binary' }
+
+/**
+ * DB is a thin wrapper around the underlying levelup db,
+ * which validates inputs and sets encoding type.
+ */
+module.exports = class DB {
+  /**
+   * Initialize a DB instance. If `leveldb` is not provided, DB
+   * defaults to an [in-memory store](https://github.com/Level/memdown).
+   * @param {Object} [leveldb] - An abstract-leveldown compliant store
+   */
+  constructor (leveldb) {
+    this._leveldb = leveldb || level()
+  }
+
+  /**
+   * Retrieves a raw value from leveldb.
+   * @param {Buffer} key
+   * @param {Function} cb A callback `Function`, which is given the arguments
+   * `err` - for errors that may have occured
+   * and `value` - the found value in a `Buffer` or if no value was found `null`.
+   */
+  get (key, cb) {
+    if (!Buffer.isBuffer(key)) throw new Error('Invalid input: expected buffer')
+
+    this._leveldb.get(key, ENCODING_OPTS, (err, v) => {
+      if (err || !v) {
+        cb(null, null)
+      } else {
+        cb(null, v)
+      }
+    })
+  }
+
+  /**
+   * Writes a value directly to leveldb.
+   * @param {Buffer} key The key as a `Buffer` or `String`
+   * @param {Buffer} value The value to be stored
+   * @param {Function} cb A callback `Function`, which is given the argument
+   * `err` - for errors that may have occured
+   */
+  put (key, val, cb) {
+    if (!Buffer.isBuffer(key)) throw new Error('Invalid input: expected buffer')
+    if (!Buffer.isBuffer(val)) throw new Error('Invalid input: expected buffer')
+
+    this._leveldb.put(key, val, ENCODING_OPTS, cb)
+  }
+
+  /**
+   * Removes a raw value in the underlying leveldb.
+   * @param {Buffer} key
+   * @param {Function} cb A callback `Function`, which is given the argument
+   * `err` - for errors that may have occured
+   */
+  del (key, cb) {
+    if (!Buffer.isBuffer(key)) throw new Error('Invalid input: expected buffer')
+
+    this._leveldb.del(key, ENCODING_OPTS, cb)
+  }
+
+  /**
+   * Performs a batch operation on db.
+   * @param {Array} opStack A stack of levelup operations
+   * @param {Function} cb A callback `Function`, which is given the argument
+   * `err` - for errors that may have occured
+   */
+  batch (opStack, cb) {
+    if (!Array.isArray(opStack)) throw new Error('Invalid input: expected buffer')
+
+    this._leveldb.batch(opStack, ENCODING_OPTS, cb)
+  }
+
+  /**
+   * Returns a copy of the DB instance, with a reference
+   * to the **same** underlying leveldb instance.
+   */
+  copy () {
+    return new DB(this._leveldb)
+  }
+}
diff --git a/src/index.js b/src/index.js
index bcbc04b..dd7bc96 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1 +1 @@
-module.exports = require('./checkpoint-trie')
+module.exports = require('./checkpointTrie')
diff --git a/src/scratch.js b/src/scratch.js
new file mode 100644
index 0000000..d6ec9b2
--- /dev/null
+++ b/src/scratch.js
@@ -0,0 +1,42 @@
+const DB = require('./db')
+const { asyncFirstSeries } = require('./util/async')
+
+const ENCODING_OPTS = { keyEncoding: 'binary', valueEncoding: 'binary' }
+
+/**
+ * An in-memory wrap over `DB` with an upstream DB
+ * which will be queried when a key is not found
+ * in the in-memory scratch. This class is used to implement
+ * checkpointing functionality in CheckpointTrie.
+ */
+module.exports = class ScratchDB extends DB {
+  constructor (upstreamDB) {
+    super()
+    this._upstream = upstreamDB
+  }
+
+  /**
+   * Similar to `DB.get`, but first searches in-memory
+   * scratch DB, if key not found, searches upstream DB.
+   */
+  get (key, cb) {
+    const getDBs = this._upstream._leveldb ? [this._leveldb, this._upstream._leveldb] : [this._leveldb]
+    const dbGet = (db, cb2) => {
+      db.get(key, ENCODING_OPTS, (err, v) => {
+        if (err || !v) {
+          cb2(null, null)
+        } else {
+          cb2(null, v)
+        }
+      })
+    }
+
+    asyncFirstSeries(getDBs, dbGet, cb)
+  }
+
+  copy () {
+    const scratch = new ScratchDB(this._upstream)
+    scratch._leveldb = this._leveldb
+    return scratch
+  }
+}
diff --git a/src/secure.js b/src/secure.js
index 78f60aa..9a62f63 100644
--- a/src/secure.js
+++ b/src/secure.js
@@ -1,5 +1,5 @@
 const ethUtil = require('ethereumjs-util')
-const CheckpointTrie = require('./checkpoint-trie')
+const CheckpointTrie = require('./checkpointTrie')
 
 /**
  * You can create a secure Trie where the keys are automatically hashed
@@ -15,7 +15,8 @@ module.exports = class SecureTrie extends CheckpointTrie {
   }
 
   copy () {
-    return new SecureTrie(this.db, this.root)
+    const db = this.db.copy()
+    return new SecureTrie(db, this.root)
   }
 
   get (key, cb) {
diff --git a/test/checkpoint.js b/test/checkpoint.js
new file mode 100644
index 0000000..21aba13
--- /dev/null
+++ b/test/checkpoint.js
@@ -0,0 +1,128 @@
+const tape = require('tape')
+const Trie = require('../src/checkpointTrie')
+
+tape('testing checkpoints', function (tester) {
+  let trie, preRoot, postRoot, trieCopy
+  const it = tester.test
+
+  it('setup', function (t) {
+    trie = new Trie()
+    trie.put('do', 'verb', function () {
+      trie.put('doge', 'coin', function () {
+        preRoot = trie.root.toString('hex')
+        t.end()
+      })
+    })
+  })
+
+  it('should copy trie and get value before checkpoint', function (t) {
+    trieCopy = trie.copy()
+    t.equal(trieCopy.root.toString('hex'), preRoot)
+    trieCopy.get('do', function (err, res) {
+      t.error(err)
+      t.ok(Buffer.from('verb').equals(res))
+      t.end()
+    })
+  })
+
+  it('should create a checkpoint', function (t) {
+    trie.checkpoint()
+    t.end()
+  })
+
+  it('should save to the cache', function (t) {
+    trie.put('test', 'something', function () {
+      trie.put('love', 'emotion', function () {
+        postRoot = trie.root.toString('hex')
+        t.end()
+      })
+    })
+  })
+
+  it('should get values from before checkpoint', function (t) {
+    trie.get('doge', function (err, res) {
+      t.error(err)
+      t.ok(Buffer.from('coin').equals(res))
+      t.end()
+    })
+  })
+
+  it('should get values from cache', function (t) {
+    trie.get('love', function (err, res) {
+      t.error(err)
+      t.ok(Buffer.from('emotion').equals(res))
+      t.end()
+    })
+  })
+
+  it('should copy trie and get upstream and cache values after checkpoint', function (t) {
+    trieCopy = trie.copy()
+    t.equal(trieCopy.root.toString('hex'), postRoot)
+    t.equal(trieCopy._checkpoints.length, 1)
+    t.ok(trieCopy.isCheckpoint)
+    trieCopy.get('do', function (err, res) {
+      t.error(err)
+      t.ok(Buffer.from('verb').equals(res))
+      trieCopy.get('love', function (err, res) {
+        t.error(err)
+        t.ok(Buffer.from('emotion').equals(res))
+        t.end()
+      })
+    })
+  })
+
+  it('should revert to the orginal root', function (t) {
+    t.equal(trie.isCheckpoint, true)
+    trie.revert(function () {
+      t.equal(trie.root.toString('hex'), preRoot)
+      t.equal(trie.isCheckpoint, false)
+      t.end()
+    })
+  })
+
+  it('should not get values from cache after revert', function (t) {
+    trie.get('love', function (err, res) {
+      t.error(err)
+      t.notOk(res)
+      t.end()
+    })
+  })
+
+  it('should commit a checkpoint', function (t) {
+    trie.checkpoint()
+    trie.put('test', 'something', function () {
+      trie.put('love', 'emotion', function () {
+        trie.commit(function () {
+          t.equal(trie.isCheckpoint, false)
+          t.equal(trie.root.toString('hex'), postRoot)
+          t.end()
+        })
+      })
+    })
+  })
+
+  it('should get new values after commit', function (t) {
+    trie.get('love', function (err, res) {
+      t.error(err)
+      t.ok(Buffer.from('emotion').equals(res))
+      t.end()
+    })
+  })
+
+  it('should commit a nested checkpoint', function (t) {
+    trie.checkpoint()
+    var root
+    trie.put('test', 'something else', function () {
+      root = trie.root
+      trie.checkpoint()
+      trie.put('the feels', 'emotion', function () {
+        trie.revert()
+        trie.commit(function () {
+          t.equal(trie.isCheckpoint, false)
+          t.equal(trie.root.toString('hex'), root.toString('hex'))
+          t.end()
+        })
+      })
+    })
+  })
+})
diff --git a/test/db.js b/test/db.js
new file mode 100644
index 0000000..2f69128
--- /dev/null
+++ b/test/db.js
@@ -0,0 +1,55 @@
+const tape = require('tape')
+const DB = require('../src/db')
+
+tape('DB basic functionality', (t) => {
+  const db = new DB()
+
+  const k = Buffer.from('foo')
+  const v = Buffer.from('bar')
+
+  t.test('puts and gets value', (st) => {
+    db.put(k, v, () => {
+      db.get(k, (err, res) => {
+        st.error(err)
+        st.ok(v.equals(res))
+        st.end()
+      })
+    })
+  })
+
+  t.test('dels value', (st) => {
+    db.del(k, () => {
+      db.get(k, (err, res) => {
+        st.error(err)
+        st.notOk(res)
+        st.end()
+      })
+    })
+  })
+
+  t.test('batch ops', (st) => {
+    const k2 = Buffer.from('bar')
+    const v2 = Buffer.from('baz')
+    const ops = [{ type: 'put', key: k, value: v }, { type: 'put', key: k2, value: v2 }]
+    db.batch(ops, (err) => {
+      st.error(err)
+      db.get(k2, (err, res) => {
+        st.error(err)
+        st.ok(v2.equals(res))
+        st.end()
+      })
+    })
+  })
+})
+
+tape('DB input types', (t) => {
+  const db = new DB()
+
+  t.test('fails for invalid input', (st) => {
+    try {
+      db.get('test')
+    } catch (e) {
+      st.end()
+    }
+  })
+})
diff --git a/test/index.js b/test/index.js
index b0bf9bc..c5256f3 100644
--- a/test/index.js
+++ b/test/index.js
@@ -229,74 +229,6 @@ tape('testing deletions cases', function (tester) {
   })
 })
 
-tape('testing checkpoints', function (tester) {
-  var trie, preRoot, postRoot
-  var it = tester.test
-
-  it('setup', function (t) {
-    trie = new Trie()
-    trie.put('do', 'verb', function () {
-      trie.put('doge', 'coin', function () {
-        preRoot = trie.root.toString('hex')
-        t.end()
-      })
-    })
-  })
-
-  it('should create a checkpoint', function (t) {
-    trie.checkpoint()
-    t.end()
-  })
-
-  it('should save to the cache', function (t) {
-    trie.put('test', 'something', function () {
-      trie.put('love', 'emotion', function () {
-        postRoot = trie.root.toString('hex')
-        t.end()
-      })
-    })
-  })
-
-  it('should revert to the orginal root', function (t) {
-    t.equal(trie.isCheckpoint, true)
-    trie.revert(function () {
-      t.equal(trie.root.toString('hex'), preRoot)
-      t.equal(trie.isCheckpoint, false)
-      t.end()
-    })
-  })
-
-  it('should commit a checkpoint', function (t) {
-    trie.checkpoint()
-    trie.put('test', 'something', function () {
-      trie.put('love', 'emotion', function () {
-        trie.commit(function () {
-          t.equal(trie.isCheckpoint, false)
-          t.equal(trie.root.toString('hex'), postRoot)
-          t.end()
-        })
-      })
-    })
-  })
-
-  it('should commit a nested checkpoint', function (t) {
-    trie.checkpoint()
-    var root
-    trie.put('test', 'something else', function () {
-      root = trie.root
-      trie.checkpoint()
-      trie.put('the feels', 'emotion', function () {
-        trie.revert()
-        trie.commit(function () {
-          t.equal(trie.isCheckpoint, false)
-          t.equal(trie.root.toString('hex'), root.toString('hex'))
-          t.end()
-        })
-      })
-    })
-  })
-})
-
 tape('it should create the genesis state root from ethereum', function (tester) {
   var it = tester.test
   var trie4 = new Trie()
diff --git a/test/rawOPs.js b/test/rawOPs.js
deleted file mode 100644
index 26b2e12..0000000
--- a/test/rawOPs.js
+++ /dev/null
@@ -1,71 +0,0 @@
-const Trie = require('../src/index.js')
-const tape = require('tape')
-const crypto = require('crypto')
-
-tape('put & get raw functions', function (it) {
-  var trie = new Trie()
-  var key = crypto.randomBytes(32)
-  var val = crypto.randomBytes(32)
-
-  it.test('putRaw', function (t) {
-    trie.putRaw(key, val, t.end)
-  })
-
-  it.test('getRaw', function (t) {
-    trie.getRaw(key, function (err, rVal) {
-      t.equal(val.toString('hex'), rVal.toString('hex'))
-      t.end(err)
-    })
-  })
-
-  it.test('should checkpoint and get the rawVal', function (t) {
-    trie.checkpoint()
-    trie.getRaw(key, function (err, rVal) {
-      t.equal(val.toString('hex'), rVal.toString('hex'))
-      t.end(err)
-    })
-  })
-
-  var key2 = crypto.randomBytes(32)
-  var val2 = crypto.randomBytes(32)
-  it.test('should store while in a checkpoint', function (t) {
-    trie.putRaw(key2, val2, t.end)
-  })
-
-  it.test('should retrieve from a checkpoint', function (t) {
-    trie.getRaw(key2, function (err, rVal) {
-      t.equal(val2.toString('hex'), rVal.toString('hex'))
-      t.end(err)
-    })
-  })
-
-  it.test('should not retiev after revert', function (t) {
-    trie.revert(t.end)
-  })
-
-  it.test('should delete raw', function (t) {
-    trie.delRaw(val2, t.end)
-  })
-
-  it.test('should not get val after delete ', function (t) {
-    trie.getRaw(val2, function (err, val) {
-      t.notok(val)
-      t.end(err)
-    })
-  })
-
-  var key3 = crypto.randomBytes(32)
-  var val3 = crypto.randomBytes(32)
-
-  it.test('test commit behavoir', function (t) {
-    trie.checkpoint()
-    trie.putRaw(key3, val3, function () {
-      trie.commit(function () {
-        trie.getRaw(key3, function (err, val) {
-          t.equal(val.toString('hex'), val3.toString('hex'))
-          t.end(err)
-        })
-      })
-    })
-  })
-})
diff --git a/test/scratch.js b/test/scratch.js
new file mode 100644
index 0000000..5be8aa6
--- /dev/null
+++ b/test/scratch.js
@@ -0,0 +1,57 @@
+const tape = require('tape')
+const ScratchDB = require('../src/scratch')
+const DB = require('../src/db')
+
+tape('ScratchDB', (t) => {
+  const upstream = new DB()
+  const scratch = new ScratchDB(upstream)
+
+  const k = Buffer.from('foo')
+  const v = Buffer.from('bar')
+  const k2 = Buffer.from('bar')
+  const v2 = Buffer.from('baz')
+
+  t.test('should fail to get non-existent value', (st) => {
+    scratch.get(k, (err, res) => {
+      st.error(err)
+      st.notOk(res)
+      st.end()
+    })
+  })
+
+  t.test('puts value to scratch', (st) => {
+    scratch.put(k, v, () => {
+      scratch.get(k, (err, res) => {
+        st.error(err)
+        st.ok(v.equals(res))
+        st.end()
+      })
+    })
+  })
+
+  t.test('should not have put value to upstream', (st) => {
+    upstream.get(k, (err, res) => {
+      st.error(err)
+      st.notOk(res)
+      st.end()
+    })
+  })
+
+  t.test('should put value directly to upstream', (st) => {
+    upstream.put(k2, v2, () => {
+      upstream.get(k2, (err, res) => {
+        st.error(err)
+        st.ok(v2.equals(res))
+        st.end()
+      })
+    })
+  })
+
+  t.test('scratch should get value from upstream', (st) => {
+    scratch.get(k2, (err, res) => {
+      st.error(err)
+      st.ok(v2.equals(res))
+      st.end()
+    })
+  })
+})
diff --git a/test/secure.js b/test/secure.js
index aa62c91..f251df4 100644
--- a/test/secure.js
+++ b/test/secure.js
@@ -2,10 +2,36 @@ const Trie = require('../src/secure.js')
 const async = require('async')
 const tape = require('tape')
 
-var trie = new Trie()
+
+tape('SecureTrie', function (t) {
+  const trie = new Trie()
+  const k = Buffer.from('foo')
+  const v = Buffer.from('bar')
+
+  t.test('put and get value', function (st) {
+    trie.put(k, v, function () {
+      trie.get(k, function (err, res) {
+        st.error(err)
+        st.ok(v.equals(res))
+        st.end()
+      })
+    })
+  })
+
+  t.test('copy trie', function (st) {
+    const t = trie.copy()
+    t.get(k, function (err, res) {
+      st.error(err)
+      st.ok(v.equals(res))
+      st.end()
+    })
+  })
+})
 
 tape('secure tests', function (it) {
+  let trie = new Trie()
   const jsonTests = require('./fixture/trietest_secureTrie.json').tests
+
   it.test('empty values', function (t) {
     async.eachSeries(jsonTests.emptyValues.in, function (row, cb) {
       trie.put(new Buffer(row[0]), row[1], cb)
diff --git a/test/streams.js b/test/streams.js
index e6eaa83..bf1d5f7 100644
--- a/test/streams.js
+++ b/test/streams.js
@@ -141,7 +141,7 @@ describe('db stream test', function (tester) {
   })
 
   it('should only fetch nodes in the current trie', function (t) {
-    var stream = trie.createScratchReadStream()
+    var stream = trie._createScratchReadStream()
     stream.on('data', function (d) {
       var key = d.key.toString('hex')
       t.ok(!!expectedNodes[key])