Make matplotlib.testing assume pytest by default, not nose.

anntzer · anntzer · commit bba95a003dde · 2019-04-10T09:22:58.000+02:00
Currently, matplotlib.testing generates nose-based tests (through the
deprecated ImageComparisonTest class and nose.SkipTest), unless one is
actually running tests with pytest (so that matplotlib.testing.conftest
has been run).

This means that e.g. importing `matplotlib.tests.test_foo` will fail if
nose is not installed (because we'll try to import nose.tools).

Given that both support for nose in Matplotlib and nose itself are
deprecated, invert the logic to generate pytest-base tests unless
both matplotlib.testing.conftest has *not* been run by pytest, and
"nose" is already in sys.modules.

Also change the default value of the "obj_type" parameter from
"attribute" to cbook.warn_deprecated to the empty string (the previous
default was never used, and the empty string as default is practical
e.g. in the case in this PR).
diff --git a/doc/api/next_api_changes/2019-04-09-AL.rst b/doc/api/next_api_changes/2019-04-09-AL.rst
@@ -0,0 +1,19 @@
+Deprecations
+````````````
+
+Support in `matplotlib.testing` for nose-based tests is deprecated (a
+deprecation is emitted if using e.g. the decorators from that module while
+both 1) matplotlib's conftests have not been called and 2) nose is in
+``sys.modules``).
+
+``testing.is_called_from_pytest`` is deprecated.
+
+During the deprecation period, to force the generation of nose base tests,
+import nose first.
+
+API changes
+```````````
+
+The default value of the "obj_type" parameter to ``cbook.warn_deprecated`` has
+been changed from "attribute" (a default that was never used internally) to the
+empty string.
diff --git a/lib/matplotlib/cbook/deprecation.py b/lib/matplotlib/cbook/deprecation.py
@@ -22,8 +22,8 @@ class MatplotlibDeprecationWarning(UserWarning):
 
 
 def _generate_deprecation_warning(
-        since, message='', name='', alternative='', pending=False,
-        obj_type='attribute', addendum='', *, removal=''):
+        since, message='', name='', alternative='', pending=False, obj_type='',
+        addendum='', *, removal=''):
     if pending:
         if removal:
             raise ValueError(
@@ -55,7 +55,7 @@ def _generate_deprecation_warning(
 
 def warn_deprecated(
         since, *, message='', name='', alternative='', pending=False,
-        obj_type='attribute', addendum='', removal=''):
+        obj_type='', addendum='', removal=''):
     """
     Used to display deprecation in a standard way.
 
diff --git a/lib/matplotlib/testing/__init__.py b/lib/matplotlib/testing/__init__.py
@@ -3,6 +3,7 @@
 """
 import locale
 import logging
+import sys
 import warnings
 
 import matplotlib as mpl
@@ -11,11 +12,20 @@
 _log = logging.getLogger(__name__)
 
 
+@cbook.deprecated("3.2")
 def is_called_from_pytest():
     """Whether we are in a pytest run."""
     return getattr(mpl, '_called_from_pytest', False)
 
 
+def _wants_nose():
+    wants_nose = (not getattr(mpl, '_called_from_pytest', False)
+                  and 'nose' in sys.modules)
+    if wants_nose:
+        cbook.warn_deprecated("3.2", name="support for nose-based tests")
+    return wants_nose
+
+
 def set_font_settings_for_testing():
     mpl.rcParams['font.family'] = 'DejaVu Sans'
     mpl.rcParams['text.hinting'] = False
diff --git a/lib/matplotlib/testing/compare.py b/lib/matplotlib/testing/compare.py
@@ -311,13 +311,12 @@ def convert(filename, cache):
     base, extension = filename.rsplit('.', 1)
     if extension not in converter:
         reason = "Don't know how to convert %s files to png" % extension
-        from . import is_called_from_pytest
-        if is_called_from_pytest():
-            import pytest
-            pytest.skip(reason)
-        else:
+        if mpl.testing._wants_nose():
             from nose import SkipTest
             raise SkipTest(reason)
+        else:
+            import pytest
+            pytest.skip(reason)
     newname = base + '_' + extension + '.png'
     if not os.path.exists(filename):
         raise IOError("'%s' does not exist" % filename)
diff --git a/lib/matplotlib/testing/decorators.py b/lib/matplotlib/testing/decorators.py
@@ -403,19 +403,19 @@ def image_comparison(baseline_images, extensions=None, tol=0,
         #default no kwargs to savefig
         savefig_kwarg = dict()
 
-    if is_called_from_pytest():
-        return _pytest_image_comparison(
-            baseline_images=baseline_images, extensions=extensions, tol=tol,
-            freetype_version=freetype_version, remove_text=remove_text,
-            savefig_kwargs=savefig_kwarg, style=style)
-    else:
+    if mpl.testing._wants_nose():
         if baseline_images is None:
             raise ValueError('baseline_images must be specified')
 
         return ImageComparisonTest(
             baseline_images=baseline_images, extensions=extensions, tol=tol,
             freetype_version=freetype_version, remove_text=remove_text,
             savefig_kwargs=savefig_kwarg, style=style)
+    else:
+        return _pytest_image_comparison(
+            baseline_images=baseline_images, extensions=extensions, tol=tol,
+            freetype_version=freetype_version, remove_text=remove_text,
+            savefig_kwargs=savefig_kwarg, style=style)
 
 
 def check_figures_equal(*, extensions=("png", "pdf", "svg"), tol=0):
