added hmget feature (#49)

src/commands/hmget.js

@@ -0,0 +1,3 @@
+export function hmget(key, ...fields) {
+  return fields.map(field => this.data[key][field] || null);
+}

src/commands/index.js

@@ -7,6 +7,7 @@ export * from './get';
 export * from './getset';
 export * from './hget';
 export * from './hgetall';
+export * from './hmget';
 export * from './hmset';
 export * from './hset';
 export * from './hsetnx';

test/commands/hmget.js

@@ -0,0 +1,17 @@
+import expect from 'expect';
+
+import MockRedis from '../../src';
+
+describe('hmget', () => {
+  it('should return the values of specified keys in a hash map', () => {
+    const redis = new MockRedis({
+      data: {
+        'user:1': { id: '1', email: '[email protected]' },
+      },
+    });
+    return redis.hmget('user:1', 'id', 'email', 'location')
+         .then(values => expect(values).toEqual([
+           '1', '[email protected]', null,
+         ]));
+  });
+});