Add a dummy non-empty environment when using assert_python_{failure,ok}

If the env_vars argument to assert_python_failure or assert_python_ok
is empty the test will run in isolated mode (-I) which means that the
PYTHONPATH environment variable will be ignored and the test fails
because the isal module can not be found, or the test is run usung the
system installed version of the module instead of the newly built
module that should be tested.

By adding a dummy entry to the env_vars argument the isolated mode is
not used and the PYTHONPATH environment variable is not ignored and
the test works as expected.

Author: ellert

CHANGELOG.rst

@@ -8,6 +8,10 @@ Changelog
 .. that users understand how the changes affect the new version.
 
 
+version 1.7.3
+-----------------
++ Fix an issue where some tests failed because they ignored PYTHONPATH.
+
 version 1.7.2
 -----------------
 + Use upstream ISA-L version 2.31.1 which includes patches to make 

tests/test_gzip_compliance.py

@@ -847,7 +847,8 @@ def test_decompress_infile_outfile(self):
 
     def test_decompress_infile_outfile_error(self):
         rc, out, err = assert_python_failure('-m', 'isal.igzip', '-d',
-                                             'thisisatest.out')
+                                             'thisisatest.out',
+                                             **{'_dummy': '1'})
         self.assertEqual(b"filename doesn't end in .gz: 'thisisatest.out'. "
                          b"Cannot determine output filename.",
                          err.strip())
@@ -872,7 +873,8 @@ def test_compress_infile_outfile_default(self):
         with open(local_testigzip, 'wb') as fp:
             fp.write(self.data)
 
-        rc, out, err = assert_python_ok('-m', 'isal.igzip', local_testigzip)
+        rc, out, err = assert_python_ok('-m', 'isal.igzip', local_testigzip,
+                                        **{'_dummy': '1'})
 
         self.assertTrue(os.path.exists(igzipname))
         self.assertEqual(out, b'')
@@ -891,7 +893,8 @@ def test_compress_infile_outfile(self):
 
                 rc, out, err = assert_python_ok('-m', 'isal.igzip',
                                                 compress_level,
-                                                local_testigzip)
+                                                local_testigzip,
+                                                **{'_dummy': '1'})
 
                 self.assertTrue(os.path.exists(igzipname))
                 self.assertEqual(out, b'')
@@ -901,15 +904,15 @@ def test_compress_infile_outfile(self):
 
     def test_compress_fast_best_are_exclusive(self):
         rc, out, err = assert_python_failure('-m', 'isal.igzip', '--fast',
-                                             '--best')
+                                             '--best', **{'_dummy': '1'})
         self.assertIn(
             b"error: argument -3/--best: not allowed with argument -0/--fast",
             err)
         self.assertEqual(out, b'')
 
     def test_decompress_cannot_have_flags_compression(self):
         rc, out, err = assert_python_failure('-m', 'isal.igzip', '--fast',
-                                             '-d')
+                                             '-d', **{'_dummy': '1'})
         self.assertIn(
             b'error: argument -d/--decompress: not allowed with argument '
             b'-0/--fast',