TST: update raises on duplicate arg index (pandas-dev#55509)

Author: aureliobarbosa

pandas/tests/frame/methods/test_update.py

@@ -206,3 +206,10 @@ def test_update_preserve_dtype(self, value_df, value_other, dtype):
         expected = DataFrame({"a": [value_other, value_df]}, index=[1, 2])
         df.update(other)
         tm.assert_frame_equal(df, expected)
+
+    def test_update_raises_on_duplicate_argument_index(self):
+        # GH#55509
+        df = DataFrame({"a": [True, True]}, index=[1, 2])
+        other = DataFrame({"a": [False, False]}, index=[1, 1])
+        with pytest.raises(ValueError, match="duplicate argument index"):
+            df.update(other)