Revert commits used to test Travis CI test failures.

End result of the experiment: The failure isn't related to the tests
added by this PR.

Author: tonysyu

lib/matplotlib/__init__.py

@@ -1317,6 +1317,7 @@ def tk_window_focus():
     'matplotlib.tests.test_simplification',
     'matplotlib.tests.test_spines',
     'matplotlib.tests.test_streamplot',
+    'matplotlib.tests.test_style',
     'matplotlib.tests.test_subplots',
     'matplotlib.tests.test_table',
     'matplotlib.tests.test_text',

lib/matplotlib/tests/test_style.py

@@ -0,0 +1,68 @@
+import os
+import shutil
+import tempfile
+from contextlib import contextmanager
+
+import matplotlib as mpl
+from matplotlib import style
+from matplotlib.style.core import USER_LIBRARY_PATHS, STYLE_EXTENSION
+
+
+PARAM = 'image.cmap'
+VALUE = 'pink'
+DUMMY_SETTINGS = {PARAM: VALUE}
+
+
+@contextmanager
+def temp_style(style_name, settings=None):
+    """Context manager to create a style sheet in a temporary directory."""
+    settings = DUMMY_SETTINGS
+    temp_file = '%s.%s' % (style_name, STYLE_EXTENSION)
+
+    # Write style settings to file in the temp directory.
+    tempdir = tempfile.mkdtemp()
+    with open(os.path.join(tempdir, temp_file), 'w') as f:
+        for k, v in settings.iteritems():
+            f.write('%s: %s' % (k, v))
+
+    # Add temp directory to style path and reload so we can access this style.
+    USER_LIBRARY_PATHS.append(tempdir)
+    style.reload_library()
+
+    try:
+        yield
+    finally:
+        shutil.rmtree(tempdir)
+        style.reload_library()
+
+
+def test_available():
+    with temp_style('_test_', DUMMY_SETTINGS):
+        assert '_test_' in style.available
+
+
+def test_use():
+    mpl.rcParams[PARAM] = 'gray'
+    with temp_style('test', DUMMY_SETTINGS):
+        with style.context('test'):
+            assert mpl.rcParams[PARAM] == VALUE
+
+
+def test_use_url():
+    with temp_style('test', DUMMY_SETTINGS):
+        with style.context('https://gist.github.com/adrn/6590261/raw'):
+            assert mpl.rcParams['axes.facecolor'] == "#adeade"
+
+
+def test_context():
+    mpl.rcParams[PARAM] = 'gray'
+    with temp_style('test', DUMMY_SETTINGS):
+        with style.context('test'):
+            assert mpl.rcParams[PARAM] == VALUE
+    # Check that this value is reset after the exiting the context.
+    assert mpl.rcParams[PARAM] == 'gray'
+
+
+if __name__ == '__main__':
+    from numpy import testing
+    testing.run_module_suite()