feat: implement zcard command stipsan#702 (stipsan#732)

compat.md

@@ -160,7 +160,7 @@
 | [xreadgroup](http://redis.io/commands/XREADGROUP)                     |        :x:         |        :x:         |
 | [xrevrange](http://redis.io/commands/XREVRANGE)                       |        :x:         |        :x:         |
 | [zadd](http://redis.io/commands/ZADD)                                 | :white_check_mark: | :white_check_mark: |
-| [zcard](http://redis.io/commands/ZCARD)                               | :white_check_mark: |        :x:         |
+| [zcard](http://redis.io/commands/ZCARD)                               | :white_check_mark: | :white_check_mark: |
 | [zcount](http://redis.io/commands/ZCOUNT)                             | :white_check_mark: |        :x:         |
 | [zincrby](http://redis.io/commands/ZINCRBY)                           | :white_check_mark: | :white_check_mark: |
 | [zinterstore](http://redis.io/commands/ZINTERSTORE)                   | :white_check_mark: |        :x:         |

src/commands/index.js

@@ -102,6 +102,7 @@ export * from './xrange';
 export * from './xread';
 export * from './xrevrange';
 export * from './zadd';
+export * from './zcard';
 export * from './zcount';
 export * from './zincrby';
 export * from './zrange';

src/commands/zcard.js

@@ -0,0 +1,12 @@
+import Map from 'es6-map';
+
+export function zcard(key) {
+  const map = this.data.get(key);
+  if (!map) {
+    return 0;
+  }
+  if (!(map instanceof Map)) {
+    throw new Error(`Key ${key} does not contain a sorted set`);
+  }
+  return this.data.get(key).size;
+}

test/commands/zcard.js

@@ -0,0 +1,36 @@
+import expect from 'expect';
+import Map from 'es6-map';
+
+import MockRedis from '../../src';
+
+describe('zcard', () => {
+  it('should return the number of items in the sorted set', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: new Map([[1, 'one'], [3, 'three'], [4, 'four']]),
+      },
+    });
+
+    return redis.zcard('foo').then(length => expect(length).toBe(3));
+  });
+
+  it('should return 0 if the sorted set does not exist', () => {
+    const redis = new MockRedis();
+
+    return redis.zcard('foo').then(length => expect(length).toBe(0));
+  });
+
+  it('should throw an exception if the key contains something other than a sorted set', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: 'not a sorted set',
+      },
+    });
+
+    return redis
+      .zcard('foo')
+      .catch(err =>
+        expect(err.message).toBe('Key foo does not contain a sorted set')
+      );
+  });
+});