TST: GH26650, added new test to validate numpy matmul function with dataframes (#47427)

* TST: GH26650, added new test to validate numpy matmul function with dataframes as inputs

* TST: GH26650, updated variable names

* Updated based on PR feedback

* Removed variable initialisations per feedback

* Final updates to PR

* Update pandas/tests/series/test_ufunc.py

Co-authored-by: Matthew Roeschke <[email protected]>

Author: carbonleakage

pandas/tests/series/test_ufunc.py

@@ -439,3 +439,14 @@ def test_outer():
 
     with pytest.raises(NotImplementedError, match=tm.EMPTY_STRING_PATTERN):
         np.subtract.outer(s, o)
+
+
+def test_np_matmul():
+    # GH26650
+    df1 = pd.DataFrame(data=[[-1, 1, 10]])
+    df2 = pd.DataFrame(data=[-1, 1, 10])
+    expected_result = pd.DataFrame(data=[102])
+    tm.assert_frame_equal(
+        expected_result,
+        np.matmul(df1, df2),
+    )