Skip running the tests on Windows Debug. (#292)

* Skip running the tests on Windows Debug.

When we run CI on Windows Debug, Python expects to be able
to find compiled libraries with an extra _d in their filename
that contains the debugging ABI.

However, we don't currently have a debug library available for PyQt5,
and thus when running under Windows Debug, the tests cannot succeed.
While we could build a debug library for PyQt5, that is actually a
massive undertaking. Instead, just skip these tests when we are on
Windows Debug. While that loses us a bit of coverage, it won't matter
much; we are still testing this on Windows (Release) and on Linux.

The way in which this patch determines that this is a Windows Debug
interpreter is a little chintzy. It just uses the fact that the binary
is named python_d.exe to discover that. I couldn't find another way
to tell if this was a debug interpreter, but I am open to other ideas.

* Update to using importlib.machinery.

Thanks to Shane for figuring out this way to tell
if we are in a debug interpreter.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

Author: clalancette

qt_dotgraph/test/dot_to_qt_test.py

@@ -34,12 +34,25 @@
 # This file does not pass flake8 due to the raw string literals below.
 # flake8: noqa
 
+import importlib.machinery
 import subprocess
 import sys
 import unittest
 
-from python_qt_binding.QtWidgets import QApplication
-from qt_dotgraph.dot_to_qt import DotToQtGenerator, get_unquoted
+try:
+    from python_qt_binding.QtWidgets import QApplication
+    from qt_dotgraph.dot_to_qt import DotToQtGenerator, get_unquoted
+    qt_import_failed = False
+except ImportError:
+    # If this is running on a Python Windows interpreter built in debug mode, skip running tests
+    # because we do not have the debug libraries available for PyQt.  It is surprisingly tricky to
+    # discover whether the current interpreter was built in debug mode (note that this is different
+    # than running the interpreter in debug mode, i.e. PYTHONDEBUG=1).  The only non-deprecated way
+    # we've found is to look for _d.pyd in the extension suffixes, so that is what we do here.
+    if sys.platform == 'win32' and '_d.pyd' in importlib.machinery.EXTENSION_SUFFIXES:
+        qt_import_failed = True
+    else:
+        raise
 
 
 def check_x_server():
@@ -54,6 +67,7 @@ def check_x_server():
     return p.returncode == 0
 
 
+@unittest.skipIf(qt_import_failed, 'Skipping test on Windows Debug')
 class DotToQtGeneratorTest(unittest.TestCase):
 
     DOT_CODE = r'''