Shorten usage of @image_comparison.

```
@image_comparison(baseline_images=["foo"], extensions=["png"])
```
is quite a mouthful.  Shorten it to
```
@image_comparison(["foo.png"])
```
instead (in the common cases when either only one extension or all
extensions are tested).

The only interesting change is in `decorators.py`; the rest is just
regexps and manual changes.

Author: anntzer

lib/matplotlib/testing/decorators.py

@@ -366,6 +366,10 @@ def image_comparison(baseline_images, extensions=None, tol=0,
 
         If *None*, defaults to all supported extensions: png, pdf, and svg.
 
+        When testing a single extension, it can be directly included in the
+        names passed to *baseline_images*.  In that case, *extensions* must not
+        be set.
+
         In order to keep the size of the test suite from ballooning, we only
         include the ``svg`` or ``pdf`` outputs if the test is explicitly
         exercising a feature dependent on that backend (see also the
@@ -393,10 +397,26 @@ def image_comparison(baseline_images, extensions=None, tol=0,
         Optional name for the base style to apply to the image test. The test
         itself can also apply additional styles if desired. Defaults to the
         '_classic_test' style.
-
     """
+
+    if baseline_images is not None:
+        # List of non-empty filename extensions.
+        baseline_exts = [*filter(None, {Path(baseline).suffix[1:]
+                                        for baseline in baseline_images})]
+        if baseline_exts:
+            if extensions is not None:
+                raise ValueError(
+                    "When including extensions directly in 'baseline_images', "
+                    "'extensions' cannot be set as well")
+            if len(baseline_exts) > 1:
+                raise ValueError(
+                    "When including extensions directly in 'baseline_images', "
+                    "all baselines must share the same suffix")
+            extensions = baseline_exts
+            baseline_images = [  # Chop suffix out from baseline_images.
+                Path(baseline).stem for baseline in baseline_images]
     if extensions is None:
-        # default extensions to test
+        # Default extensions to test, if not set via baseline_images.
         extensions = ['png', 'pdf', 'svg']
 
     if savefig_kwarg is None:

lib/matplotlib/tests/test_agg.py

@@ -78,8 +78,7 @@ def test_long_path():
     fig.savefig(buff, format='png')
 
 
-@image_comparison(baseline_images=['agg_filter'],
-                  extensions=['png'], remove_text=True)
+@image_comparison(['agg_filter.png'], remove_text=True)
 def test_agg_filter():
     def smooth1d(x, window_len):
         s = np.r_[2*x[0] - x[window_len:1:-1],

lib/matplotlib/tests/test_arrow_patches.py

@@ -11,7 +11,7 @@ def draw_arrow(ax, t, r):
                                 fc="b", ec='k'))
 
 
-@image_comparison(baseline_images=['fancyarrow_test_image'])
+@image_comparison(['fancyarrow_test_image'])
 def test_fancyarrow():
     # Added 0 to test division by zero error described in issue 3930
     r = [0.4, 0.3, 0.2, 0.1, 0]
@@ -28,7 +28,7 @@ def test_fancyarrow():
             ax.tick_params(labelleft=False, labelbottom=False)
 
 
-@image_comparison(baseline_images=['boxarrow_test_image'], extensions=['png'])
+@image_comparison(['boxarrow_test_image.png'])
 def test_boxarrow():
 
     styles = mpatches.BoxStyle.get_styles()
@@ -67,8 +67,7 @@ def __prepare_fancyarrow_dpi_cor_test():
     return fig2
 
 
-@image_comparison(baseline_images=['fancyarrow_dpi_cor_100dpi'],
-                  remove_text=True, extensions=['png'],
+@image_comparison(['fancyarrow_dpi_cor_100dpi.png'], remove_text=True,
                   tol={'aarch64': 0.02}.get(platform.machine(), 0.0),
                   savefig_kwarg=dict(dpi=100))
 def test_fancyarrow_dpi_cor_100dpi():
@@ -83,8 +82,7 @@ def test_fancyarrow_dpi_cor_100dpi():
     __prepare_fancyarrow_dpi_cor_test()
 
 
-@image_comparison(baseline_images=['fancyarrow_dpi_cor_200dpi'],
-                  remove_text=True, extensions=['png'],
+@image_comparison(['fancyarrow_dpi_cor_200dpi.png'], remove_text=True,
                   tol={'aarch64': 0.02}.get(platform.machine(), 0.0),
                   savefig_kwarg=dict(dpi=200))
 def test_fancyarrow_dpi_cor_200dpi():
@@ -96,9 +94,7 @@ def test_fancyarrow_dpi_cor_200dpi():
     __prepare_fancyarrow_dpi_cor_test()
 
 
-@image_comparison(baseline_images=['fancyarrow_dash'],
-                  remove_text=True, extensions=['png'],
-                  style='default')
+@image_comparison(['fancyarrow_dash.png'], remove_text=True, style='default')
 def test_fancyarrow_dash():
     from matplotlib.patches import FancyArrowPatch
     fig, ax = plt.subplots()
@@ -122,8 +118,7 @@ def test_fancyarrow_dash():
     ax.add_patch(e2)
 
 
-@image_comparison(baseline_images=['arrow_styles'], extensions=['png'],
-                  style='mpl20', remove_text=True)
+@image_comparison(['arrow_styles.png'], style='mpl20', remove_text=True)
 def test_arrow_styles():
     styles = mpatches.ArrowStyle.get_styles()
 
@@ -139,8 +134,7 @@ def test_arrow_styles():
         ax.add_patch(patch)
 
 
-@image_comparison(baseline_images=['connection_styles'], extensions=['png'],
-                  style='mpl20', remove_text=True)
+@image_comparison(['connection_styles.png'], style='mpl20', remove_text=True)
 def test_connection_styles():
     styles = mpatches.ConnectionStyle.get_styles()
 

lib/matplotlib/tests/test_artist.py

@@ -94,7 +94,7 @@ def test_collection_transform_of_none():
     assert isinstance(c._transOffset, mtransforms.IdentityTransform)
 
 
-@image_comparison(baseline_images=["clip_path_clipping"], remove_text=True)
+@image_comparison(["clip_path_clipping"], remove_text=True)
 def test_clipping():
     exterior = mpath.Path.unit_rectangle().deepcopy()
     exterior.vertices *= 4
@@ -142,8 +142,7 @@ def test_cull_markers():
     assert len(svg.getvalue()) < 20000
 
 
-@image_comparison(baseline_images=['hatching'], remove_text=True,
-                  style='default')
+@image_comparison(['hatching'], remove_text=True, style='default')
 def test_hatching():
     fig, ax = plt.subplots(1, 1)
 
@@ -200,8 +199,7 @@ def test_remove():
     assert ax.stale
 
 
-@image_comparison(baseline_images=["default_edges"], remove_text=True,
-                  extensions=['png'], style='default')
+@image_comparison(["default_edges.png"], remove_text=True, style='default')
 def test_default_edges():
     fig, [[ax1, ax2], [ax3, ax4]] = plt.subplots(2, 2)