add positive test for LINDEX

Author: leibale

packages/client/lib/commands/LINDEX.spec.ts

@@ -10,12 +10,23 @@ describe('LINDEX', () => {
         );
     });
 
-    testUtils.testWithClient('client.lIndex', async client => {
-        assert.equal(
-            await client.lIndex('key', 0),
-            null
-        );
-    }, GLOBAL.SERVERS.OPEN);
+    describe('client.lIndex', () => {
+        testUtils.testWithClient('null', async client => {
+            assert.equal(
+                await client.lIndex('key', 0),
+                null
+            );
+        }, GLOBAL.SERVERS.OPEN);
+
+        testUtils.testWithClient('with value', async client => {
+            const [, lIndexReply] = await Promise.all([
+                client.lPush('key', 'element'),
+                client.lIndex('key', 0)
+            ]);
+
+            assert.equal(lIndexReply, 'element');
+        }, GLOBAL.SERVERS.OPEN);
+    });
 
     testUtils.testWithCluster('cluster.lIndex', async cluster => {
         assert.equal(