TST: Split test for pandas-dev#15912

Separate the test for pandas-dev#7612 and pandas-dev#22334, that are about string index,
and test for pandas-dev#15912, about multiindex.

Author: nicolas.rebena

pandas/tests/plotting/test_frame.py

@@ -2997,9 +2997,8 @@ def test_secondary_axis_font_size(self, method):
 
     @pytest.mark.slow
     def test_x_string_values_ticks(self):
-        # GH: 7612
-        # GH: 22334
-        # GH: 15912
+        # Test if string plot index have a fixed xtick position
+        # GH: 7612, GH: 22334
         df = pd.DataFrame({'sales': [3, 2, 3],
                            'visits': [20, 42, 28],
                            'day': ['Monday', 'Tuesday', 'Wednesday']})
@@ -3012,6 +3011,24 @@ def test_x_string_values_ticks(self):
         assert labels_position['Tuesday'] == 1.0
         assert labels_position['Wednesday'] == 2.0
 
+    @pytest.mark.slow
+    def test_x_multiindex_values_ticks(self):
+        # Test if multiindex plot index have a fixed xtick position
+        # GH: 15912
+        index = pd.MultiIndex.from_product([[2012, 2013], [1, 2]])
+        df = pd.DataFrame(np.random.randn(4, 2),
+                          columns=['A', 'B'],
+                          index=index)
+        ax = df.plot()
+        ax.set_xlim(-1, 4)
+        xticklabels = [t.get_text() for t in ax.get_xticklabels()]
+        labels_position = dict(zip(xticklabels, ax.get_xticks()))
+        # Testing if the label stayed at the right position
+        assert labels_position['(2012, 1)'] == 0.0
+        assert labels_position['(2012, 2)'] == 1.0
+        assert labels_position['(2013, 1)'] == 2.0
+        assert labels_position['(2013, 2)'] == 3.0
+
 
 def _generate_4_axes_via_gridspec():
     import matplotlib.pyplot as plt