added the tests with a string for transform

Author: ramvikrams

tests/test_frame.py

@@ -2081,7 +2081,11 @@ def test_groupby_and_transform() -> None:
     )
     grouped = df.groupby("A")[["C", "D"]]
     grouped1 = ser.groupby(ser > 100)
-    c1 = grouped.transform(lambda x: (x - x.mean()) / x.std())
-    c2 = grouped1.transform(lambda x: x.max() - x.min())
+    c1 = grouped.transform("sum")
+    c2 = grouped.transform(lambda x: (x - x.mean()) / x.std())
+    c3 = grouped1.transform("cumsum")
+    c4 = grouped1.transform(lambda x: x.max() - x.min())
     check(assert_type(c1, pd.DataFrame), pd.DataFrame)
-    check(assert_type(c2, pd.Series), pd.Series)
+    check(assert_type(c2, pd.DataFrame), pd.DataFrame)
+    check(assert_type(c3, pd.Series), pd.Series)
+    check(assert_type(c4, pd.Series), pd.Series)