diff --git a/pandas/tests/groupby/test_api_consistency.py b/pandas/tests/groupby/test_api_consistency.py
index bd29f29719494..d62ee3593cd44 100644
--- a/pandas/tests/groupby/test_api_consistency.py
+++ b/pandas/tests/groupby/test_api_consistency.py
@@ -21,17 +21,22 @@ def test_frame_consistency(request, groupby_func):
     if groupby_func in ("first", "last"):
         msg = "first and last are entirely different between frame and groupby"
         request.node.add_marker(pytest.mark.xfail(reason=msg))
-    if groupby_func in ("nth", "cumcount", "ngroup"):
+    if groupby_func in ("cumcount",):
         msg = "DataFrame has no such method"
         request.node.add_marker(pytest.mark.xfail(reason=msg))
-    if groupby_func in ("size",):
-        msg = "Method is a property"
-        request.node.add_marker(pytest.mark.xfail(reason=msg))
+
+    if groupby_func == "ngroup":
+        assert not hasattr(DataFrame, groupby_func)
+        return
 
     frame_method = getattr(DataFrame, groupby_func)
     gb_method = getattr(DataFrameGroupBy, groupby_func)
     result = set(inspect.signature(gb_method).parameters)
-    expected = set(inspect.signature(frame_method).parameters)
+    if groupby_func == "size":
+        # "size" is a method on GroupBy but property on DataFrame:
+        expected = {"self"}
+    else:
+        expected = set(inspect.signature(frame_method).parameters)
 
     # Exclude certain arguments from result and expected depending on the operation
     # Some of these may be purposeful inconsistencies between the APIs
@@ -79,17 +84,22 @@ def test_series_consistency(request, groupby_func):
     if groupby_func in ("first", "last"):
         msg = "first and last are entirely different between Series and groupby"
         request.node.add_marker(pytest.mark.xfail(reason=msg))
-    if groupby_func in ("nth", "cumcount", "ngroup", "corrwith"):
+    if groupby_func in ("cumcount", "corrwith"):
         msg = "Series has no such method"
         request.node.add_marker(pytest.mark.xfail(reason=msg))
-    if groupby_func in ("size",):
-        msg = "Method is a property"
-        request.node.add_marker(pytest.mark.xfail(reason=msg))
+
+    if groupby_func == "ngroup":
+        assert not hasattr(Series, groupby_func)
+        return
 
     series_method = getattr(Series, groupby_func)
     gb_method = getattr(SeriesGroupBy, groupby_func)
     result = set(inspect.signature(gb_method).parameters)
-    expected = set(inspect.signature(series_method).parameters)
+    if groupby_func == "size":
+        # "size" is a method on GroupBy but property on Series
+        expected = {"self"}
+    else:
+        expected = set(inspect.signature(series_method).parameters)
 
     # Exclude certain arguments from result and expected depending on the operation
     # Some of these may be purposeful inconsistencies between the APIs