Add support for JSON.MERGE (#2511)

* Support JSON.MERGE Command

* test only 2.6+ ReJson version

* test on edge

* review

* Update test-utils.ts

---------

Co-authored-by: Leibale Eidelman <me@leibale.com>

packages/json/lib/commands/MERGE.spec.ts

@@ -0,0 +1,21 @@
+import { strict as assert } from 'assert';
+import testUtils, { GLOBAL } from '../test-utils';
+import { transformArguments } from './MERGE';
+
+describe('MERGE', () => {
+    testUtils.isVersionGreaterThanHook([2, 6]);
+
+    it('transformArguments', () => {
+        assert.deepEqual(
+            transformArguments('key', '$', 1),
+            ['JSON.MERGE', 'key', '$', '1']
+        );
+    });
+
+    testUtils.testWithClient('client.json.merge', async client => {
+        assert.equal(
+            await client.json.merge('key', '$', 'json'),
+            'OK'
+        );
+    }, GLOBAL.SERVERS.OPEN);
+});