add asserts to test merge function module string is set to 'pandas'

Author: chanshing

pandas/tests/api/test_api.py

@@ -416,3 +416,6 @@ def test_set_module():
     assert pd.Period.__module__ == "pandas"
     assert pd.Timestamp.__module__ == "pandas"
     assert pd.Timedelta.__module__ == "pandas"
+    assert pd.merge.__module__ == "pandas"
+    assert pd.merge_ordered.__module__ == "pandas"
+    assert pd.merge_asof.__module__ == "pandas"