TST: add tests for ValueError paths

tacaswell · tacaswell · commit e73c1a965600 · 2020-03-04T23:20:16.000-05:00
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -1650,7 +1650,10 @@ def _do_layout(gs, layout, unique_ids, nested):
                 slc = (slice(start_row, end_row), slice(start_col, end_col))
 
                 if (layout[slc] != name).any():
-                    raise ValueError
+                    raise ValueError(
+                        f"While trying to layout\n{layout!r}\n"
+                        f"we found that the label {name!r} specifies an "
+                        "impossible axes.")
 
                 if hasattr(name, 'set_subplotspec'):
                     ax = name
@@ -1662,13 +1665,17 @@ def _do_layout(gs, layout, unique_ids, nested):
                     output[name] = self.add_subplot(
                         gs[slc], **{'label': str(name), **subplot_kw})
 
-            for (j, k), layout in nested.items():
-                layout = np.asarray(layout)
-                rows, cols = layout.shape
+            for (j, k), nested_layout in nested.items():
+                nested_layout = np.asarray(nested_layout, dtype=object)
+                rows, cols = nested_layout.shape
                 gs_n = gs[j, k].subgridspec(rows, cols, **gridspec_kw)
-                nested_output = _do_layout(gs_n, layout,
-                                           *_process_layout(layout))
-
+                nested_output = _do_layout(gs_n, nested_layout,
+                                           *_process_layout(nested_layout))
+                if set(output) & set(nested_output):
+                    overlap = set(output) & set(nested_output)
+                    raise ValueError(f"There are duplicate keys {overlap} "
+                                     f"between the outer layout\n{layout!r}\n"
+                                     f"and the nested layout\n{nested_layout}")
                 output.update(nested_output)
             return output
 
diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
@@ -629,3 +629,19 @@ def test_subplot_kw(self, fig_test, fig_ref, subplot_kw):
         axA = fig_ref.add_subplot(gs[0, 0], **subplot_kw)
 
         axB = fig_ref.add_subplot(gs[0, 1], **subplot_kw)
+
+    @pytest.mark.parametrize('x,match', [
+        ([['A', None], [None, 'A']],
+         "(?m)we found that the label .A. specifies an impossible axes."),
+        ([['A', 'B'], [None, [['A', 'B'], ['C', 'D']]]],
+         # This more specific test fails 1/3 times
+         # "There are duplicate keys {.B., .A.} between the outer layout"
+         "There are duplicate keys .* between the outer layout"
+         )
+        ])
+    def test_fail(self, x, match):
+        fig = plt.figure()
+        with pytest.raises(
+                ValueError,
+                match=match):
+            fig.build_grid(x)
