diff --git a/superset/assets/javascripts/explore/stores/visTypes.js b/superset/assets/javascripts/explore/stores/visTypes.js
index 85aeff6e59a61..68991e35babf1 100644
--- a/superset/assets/javascripts/explore/stores/visTypes.js
+++ b/superset/assets/javascripts/explore/stores/visTypes.js
@@ -798,6 +798,14 @@ const visTypes = {
         ],
       },
     ],
+    controlOverrides: {
+      all_columns_x: {
+        validators: [v.nonEmpty],
+      },
+      all_columns_y: {
+        validators: [v.nonEmpty],
+      },
+    },
   },
 
   horizon: {
diff --git a/superset/cli.py b/superset/cli.py
index 46b0ca794be77..f6163bb140b09 100755
--- a/superset/cli.py
+++ b/superset/cli.py
@@ -192,7 +192,7 @@ def worker(workers):
         celery_app.conf.update(CELERYD_CONCURRENCY=workers)
     elif config.get("SUPERSET_CELERY_WORKERS"):
         celery_app.conf.update(
-            worker_concurrency=config.get("SUPERSET_CELERY_WORKERS"))
+            CELERYD_CONCURRENCY=config.get("SUPERSET_CELERY_WORKERS"))
 
     worker = celery_worker.worker(app=celery_app)
     worker.run()
diff --git a/superset/views/core.py b/superset/views/core.py
index 600207702948b..b03fef9608ad6 100755
--- a/superset/views/core.py
+++ b/superset/views/core.py
@@ -1375,7 +1375,7 @@ def testconn(self):
                 .get('connect_args', {}))
             engine = create_engine(uri, connect_args=connect_args)
             engine.connect()
-            return json.dumps(engine.table_names(), indent=4)
+            return json_success(json.dumps(engine.table_names(), indent=4))
         except Exception as e:
             logging.exception(e)
             return json_error_response((
diff --git a/tests/core_tests.py b/tests/core_tests.py
index 7ff48a9081a8c..f3e98873a63fa 100644
--- a/tests/core_tests.py
+++ b/tests/core_tests.py
@@ -284,6 +284,7 @@ def test_testconn(self):
         })
         response = self.client.post('/superset/testconn', data=data, content_type='application/json')
         assert response.status_code == 200
+        assert response.headers['Content-Type'] == 'application/json'
 
         # validate that the endpoint works with the decrypted sqlalchemy uri
         data = json.dumps({
@@ -292,6 +293,7 @@ def test_testconn(self):
         })
         response = self.client.post('/superset/testconn', data=data, content_type='application/json')
         assert response.status_code == 200
+        assert response.headers['Content-Type'] == 'application/json'
 
     def test_databaseview_edit(self, username='admin'):
         # validate that sending a password-masked uri does not over-write the decrypted uri