TST/VIZ: add test for legend colors for DataFrame with duplicate column labels #11136 (#32451)

Author: gabrielvf1

pandas/tests/plotting/test_frame.py

@@ -3316,6 +3316,16 @@ def test_missing_markers_legend_using_style(self):
         self._check_legend_labels(ax, labels=["A", "B", "C"])
         self._check_legend_marker(ax, expected_markers=[".", ".", "."])
 
+    def test_colors_of_columns_with_same_name(self):
+        # ISSUE 11136 -> https://github.com/pandas-dev/pandas/issues/11136
+        # Creating a DataFrame with duplicate column labels and testing colors of them.
+        df = pd.DataFrame({"b": [0, 1, 0], "a": [1, 2, 3]})
+        df1 = pd.DataFrame({"a": [2, 4, 6]})
+        df_concat = pd.concat([df, df1], axis=1)
+        result = df_concat.plot()
+        for legend, line in zip(result.get_legend().legendHandles, result.lines):
+            assert legend.get_color() == line.get_color()
+
 
 def _generate_4_axes_via_gridspec():
     import matplotlib.pyplot as plt