Store#add to return self

This allows for Promise chaining (and consequently temporary classes,
great for testing).

* src/store/MemoryStore.js
  (add): Resolve promise to self.
    Modify docblock.
* src/store/Store.js (add): Modify docblock.
* src/store/Cascading.js (add): Modify docblock.

* test/store/MemoryStoreTest.js: Modify test accordingly.

DEV-2296

src/store/Cascading.js

@@ -72,7 +72,8 @@ module.exports = Trait( 'Cascading' )
      * @param {string} key   store key
      * @param {Store}  value Store to attach
      *
-     * @return {Promise} promise to add item to store
+     * @return {Promise.<Store>} promise to add item to store, resolving to
+     *                           self (for chaining)
      */
     'virtual abstract override public add': function( key, value )
     {

src/store/MemoryStore.js

@@ -75,23 +75,17 @@ module.exports = Class( 'MemoryStore' )
     /**
      * Add item to store under `key` with value `value`
      *
-     * The promise will be fulfilled with an object containing the
-     * `key` and `value` added to the store; this is convenient for
-     * promises.
-     *
      * @param {string} key   store key
      * @param {*}      value value for key
      *
-     * @return {Promise} promise to add item to store
+     * @return {Promise.<Store>} promise to add item to store, resolving to
+     *                           self (for chaining)
      */
     'virtual public add': function( key, value )
     {
         this._store[ key ] = value;
 
-        return Promise.resolve( {
+        return Promise.resolve( this.__inst );
-            key:   key,
-            value: value,
-        } );
     },
 
 

src/store/Store.js

@@ -44,7 +44,8 @@ module.exports = Interface( 'Store',
      * @param {string} key   store key
      * @param {*}      value value for key
      *
-     * @return {Promise} promise to add item to store
+     * @return {Promise.<Store>} promise to add item to store, resolving to
+     *                           self (for chaining)
      */
     'public add': [ 'key', 'value' ],
 

test/store/MemoryStoreTest.js

@@ -60,14 +60,13 @@ describe( 'store.MemoryStore', () =>
         } );
 
 
-        it( 'provides the key and value of the added item', () =>
+        it( 'returns self with promise', () =>
         {
-            const key   = 'key';
+            const sut = Sut();
-            const value = 'val';
 
             return expect(
-                Sut().add( key, value )
+                sut.add( 'foo', 'bar' )
-            ).to.eventually.deep.equal( { key: key, value: value } );
+            ).to.eventually.equal( sut );
         } );
     } );