add test

Author: quangngd

pandas/tests/frame/test_stack_unstack.py

@@ -1452,6 +1452,25 @@ def test_stack_empty_frame(dropna, future_stack):
         tm.assert_series_equal(result, expected)
 
 
+@pytest.mark.filterwarnings("ignore:The previous implementation of stack is deprecated")
+@pytest.mark.parametrize("dropna", [True, False, lib.no_default])
+def test_stack_empty_level(dropna, future_stack, int_frame):
+    # GH 60740
+    if future_stack and dropna is not lib.no_default:
+        with pytest.raises(ValueError, match="dropna must be unspecified"):
+            DataFrame(dtype=np.int64).stack(dropna=dropna, future_stack=future_stack)
+    else:
+        expected = int_frame
+        result = int_frame.copy().stack(
+            level=[], dropna=dropna, future_stack=future_stack
+        )
+        tm.assert_frame_equal(result, expected)
+
+        expected = DataFrame()
+        result = DataFrame().stack(level=[], dropna=dropna, future_stack=future_stack)
+        tm.assert_frame_equal(result, expected)
+
+
 @pytest.mark.filterwarnings("ignore:The previous implementation of stack is deprecated")
 @pytest.mark.parametrize("dropna", [True, False, lib.no_default])
 @pytest.mark.parametrize("fill_value", [None, 0])