fix(test): Tests and docs for new optional API additions.

README.md

@@ -43,6 +43,21 @@ class Store {
 }
 ```
 
+There are also optional APIs. These are not required as they may not be
+possible on top of certain storage but *may* be required by certain users
+of an implementation.
+
+```javascript
+class Store {
+  set (value, ...args, cb) {
+    // Optional args are sent to the hashing function..
+  }
+  hash (value, ...args, cb) {
+    // Optional args are sent to the hashing function.
+  }
+}
+```
+
 ## In-Memory Implementation
 
 ```javascript

tests/test-fs.js

@@ -83,6 +83,21 @@ test('fs(implementation): slow hasher', t => {
   stream.end()
 })
 
+test('fs(implementation): hasher args', t => {
+  t.plan(4)
+  const argHasher = (one, two, three, cb) => {
+    t.same([one, two, three], [1, 2, 3])
+    return through(() => setTimeout(() => cb(null, 'asdf'), 100))
+  }
+  let store = fsStore(testdir, argHasher)
+  store.set(Buffer.from('asdf'), 1, 2, 3, (err, hash) => {
+    t.error(err)
+  })
+  store.hash(Buffer.from('asdf'), 1, 2, 3, (err, hash) => {
+    t.error(err)
+  })
+})
+
 let rimraf = require('rimraf')
 
 process.on('beforeExit', () => {

tests/test-inmemory.js

@@ -24,3 +24,18 @@ test('inmemory: (implementation) hash error in set()', t => {
     t.type(err, 'Error')
   })
 })
+
+test('inmemory(implementation): hasher args', t => {
+  t.plan(4)
+  const argHasher = (one, two, three, cb) => {
+    t.same([one, two, three], [1, 2, 3])
+    return through(() => setTimeout(() => cb(null, 'asdf'), 100))
+  }
+  let store = inmemory(argHasher)
+  store.set(Buffer.from('asdf'), 1, 2, 3, (err, hash) => {
+    t.error(err)
+  })
+  store.hash(Buffer.from('asdf'), 1, 2, 3, (err, hash) => {
+    t.error(err)
+  })
+})