add some missing commands

lib/commands/ECHO.spec.ts

@@ -0,0 +1,26 @@
+import { strict as assert } from 'assert';
+import { TestRedisServers, itWithClient, TestRedisClusters, itWithCluster } from '../test-utils';
+import { transformArguments } from './ECHO';
+
+describe('ECHO', () => {
+    it('transformArguments', () => {
+        assert.deepEqual(
+            transformArguments('message'),
+            ['ECHO', 'message']
+        );
+    });
+
+    itWithClient(TestRedisServers.OPEN, 'client.echo', async client => {
+        assert.equal(
+            await client.echo('message'),
+            'message'
+        );
+    });
+
+    itWithCluster(TestRedisClusters.OPEN, 'cluster.echo', async cluster => {
+        assert.equal(
+            await cluster.echo('message'),
+            'message'
+        );
+    });
+});