Report reason for pytest skips

[hugovk]

Changes proposed in this pull request:

• Show a summary of skipped tests, helps identify gaps in testing
• Add as config so no need to modify lines in several CI scripts

For example:

=========================== short test summary info ===========================
SKIPPED [2] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: Numpy is not installed
SKIPPED [2] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: images are not collected
SKIPPED [7] C:\vp\pypy2\site-packages\_pytest\unittest.py:94: olefile package not installed
SKIPPED [2] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: netpbm not available
SKIPPED [2] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: requires macOS
SKIPPED [1] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: djpeg not available
SKIPPED [1] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: cjpeg not available
SKIPPED [1] Tests\test_file_jpeg2k.py:175: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:181: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:152: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:169: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:163: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:53: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:48: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:93: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:43: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:121: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:111: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:63: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:75: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:79: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:70: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:193: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:97: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:101: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:105: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:139: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:31: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:87: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:83: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_jpeg2k.py:187: JPEG 2000 support not available
SKIPPED [1] Tests\test_file_palm.py:40: Palm P image is wrong
SKIPPED [8] C:\vp\pypy2\site-packages\_pytest\unittest.py:94: requires Unix or macOS
SKIPPED [1] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: Test requires opening tempfile twice
SKIPPED [1] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: Failing on AppVeyor when run from subprocess, not from shell
SKIPPED [1] Tests\test_image_fromqimage.py:26: Qt bindings are not installed
SKIPPED [1] Tests\test_image_fromqimage.py:38: Qt bindings are not installed
SKIPPED [1] Tests\test_image_fromqimage.py:42: Qt bindings are not installed
SKIPPED [1] Tests\test_image_fromqimage.py:30: Qt bindings are not installed
SKIPPED [1] Tests\test_image_fromqimage.py:34: Qt bindings are not installed
SKIPPED [1] Tests\test_image_quantize.py:18: libimagequant support not available
SKIPPED [2] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: current implementation isn't precise enough
SKIPPED [1] Tests\test_imagedraw.py:633: failing
SKIPPED [2] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: requires Unix or macOS
SKIPPED [1] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: requires Python 3.x on Windows
SKIPPED [38] C:\vp\pypy2\site-packages\_pytest\unittest.py:94: Raqm not Available
SKIPPED [13] C:\vp\pypy2\site-packages\_pytest\unittest.py:94: Raqm Library is not installed.
SKIPPED [1] Tests\test_imageqt.py:91: Qt bindings are not installed
SKIPPED [1] Tests\test_imageqt.py:87: Qt bindings are not installed
SKIPPED [1] Tests\test_imageqt.py:59: Qt bindings are not installed
SKIPPED [1] C:\vp\pypy2\site-packages\_pytest\unittest.py:94: Win32 does not call map_buffer
SKIPPED [12] C:\vp\pypy2\site-packages\_pytest\unittest.py:94: Numpy is not installed
SKIPPED [1] C:\vp\pypy2\site-packages\_pytest\unittest.py:94: Pyroma is not installed
SKIPPED [1] Tests\test_qt_image_fromqpixmap.py:13: Qt bindings are not installed
SKIPPED [1] Tests\test_qt_image_toqimage.py:35: Qt bindings are not installed
SKIPPED [1] Tests\test_qt_image_toqimage.py:70: Qt bindings are not installed
SKIPPED [1] Tests\test_qt_image_toqpixmap.py:11: Qt bindings are not installed
SKIPPED [1] ..\pypy2.7-v7.1.1-win32\lib-python\2.7\unittest\case.py:60: os.path support for Paths added in 3.6
================= 1218 passed, 137 skipped in 119.34 seconds ==================

The option:

$ pytest --help
...
  -r chars              show extra test summary info as specified by chars:
                        (f)ailed, (E)rror, (s)kipped, (x)failed, (X)passed,
                        (p)assed, (P)assed with output, (a)ll except passed
                        (p/P), or (A)ll. (w)arnings are enabled by default
                        (see --disable-warnings).

Edit: updated to the more usual -rs; -r s was a workaround for a Python 3.8 pytest bug, since fixed in pytest 5.0.1: pytest-dev/pytest#5523.