add mget (#134)

Awesome, I'll add you :)

src/commands/index.js

@@ -23,6 +23,7 @@ export * from './keys';
 export * from './llen';
 export * from './lpush';
 export * from './lrem';
+export * from './mget';
 export * from './publish';
 export * from './rename';
 export * from './rpoplpush';

src/commands/mget.js

@@ -0,0 +1,3 @@
+export function mget(keys) {
+  return keys.map(key => ({}.hasOwnProperty.call(this.data, key) ? this.data[key] : null));
+}

test/commands/mget.js

@@ -0,0 +1,21 @@
+import expect from 'expect';
+
+import MockRedis from '../../src';
+
+describe('mget', () => {
+  it('should return null on keys that do not exist', () => {
+    const redis = new MockRedis();
+
+    return redis.mget(['foo']).then(result => expect(result).toEqual([null]));
+  });
+
+  it('should return value keys that exist', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: 'bar',
+      },
+    });
+
+    return redis.mget(['foo', 'hello']).then(result => expect(result).toEqual(['bar', null]));
+  });
+});