diff --git a/tap_google_sheets/__init__.py b/tap_google_sheets/__init__.py
index c74f745..535f7c5 100644
--- a/tap_google_sheets/__init__.py
+++ b/tap_google_sheets/__init__.py
@@ -49,10 +49,10 @@ def main():
 
         if parsed_args.discover:
             do_discover(client, spreadsheet_id)
-        elif parsed_args.catalog:
+        else:
             sync(client=client,
                  config=config,
-                 catalog=parsed_args.catalog,
+                 catalog=parsed_args.catalog or discover(client, spreadsheet_id),
                  state=state)
 
 if __name__ == '__main__':
diff --git a/tests/unittests/test_catalog_in_sync.py b/tests/unittests/test_catalog_in_sync.py
new file mode 100644
index 0000000..76b89b1
--- /dev/null
+++ b/tests/unittests/test_catalog_in_sync.py
@@ -0,0 +1,34 @@
+import unittest
+from unittest import mock
+from tap_google_sheets import main
+
+
+class MockedParseArgs:
+    discover = False
+    config = {"client_id":"", "client_secret": "", "refresh_token": "", "user_agent": ""}
+    state = False
+    catalog = "test"
+    
+@mock.patch("tap_google_sheets.discover")
+@mock.patch("tap_google_sheets.singer.utils.parse_args", return_value=MockedParseArgs)
+@mock.patch("tap_google_sheets.GoogleClient.__enter__", return_value="test")
+@mock.patch("tap_google_sheets.sync")
+class TestCatalog(unittest.TestCase):
+    def test_catalog_is_given_in_sync(self, mocked_sync, mocked_google_client, mocked_parse_args, mocked_discover):
+        """
+        To verify that if catalog is given in sync mode then run with catalog file
+        """
+        main()
+        mocked_sync.assert_called_with(client="test", config=MockedParseArgs.config, catalog="test", state={})
+        self.assertEqual(mocked_discover.call_count, 0, "discover function is not called expected times")
+        
+    def test_catalog_is_not_given_in_sync(self, mocked_sync, mocked_google_client, mocked_parse_args, mocked_discover):
+        """
+        To verify that if catalog is not given in sync mode then run discover mode to generate catalog 
+        """
+        # mocking discover function
+        MockedParseArgs.catalog = ""
+        mocked_discover.return_value = "test"
+        main()
+        mocked_sync.assert_called_with(client="test", config=MockedParseArgs.config, catalog="test", state={})
+        self.assertEqual(mocked_discover.call_count, 1, "discover function is not called expected times")
\ No newline at end of file