another attempt at fixing appveyor

appveyor.yml

@@ -26,7 +26,7 @@ build_script:
   - git fetch --all
   - git checkout %APPVEYOR_REPO_BRANCH%
   - git reset --hard %APPVEYOR_REPO_COMMIT%
-  - git diff ..origin/master
+  - git diff --name-only origin/master
   - python -m pip install -r requirements.txt
   - cd test
     # Download Astyle to local folder because putting it in PATH doesn't work

test/helpers.py

@@ -145,12 +145,13 @@ def permit_test(testname, thing, *args, **kwargs):
 
     if 'PQCLEAN_ONLY_DIFF' in os.environ:
         if shutil.which('git') is not None:
-            # if we're on a non-master branch, and the only changes are in schemes, 
+            # if we're on a non-master branch, and the only changes are in schemes,
             # only run tests on those schemes
             branch_result = subprocess.run(
                 ['git', 'status', '--porcelain=2', '--branch'],
                 stdout=subprocess.PIPE,
-                stderr=subprocess.STDOUT
+                stderr=subprocess.STDOUT,
+                cwd="..",
             )
             # ensure we're in a working directory
             if branch_result.returncode != 0:
@@ -167,11 +168,14 @@ def permit_test(testname, thing, *args, **kwargs):
                 stdout=subprocess.PIPE,
                 stderr=subprocess.STDOUT
             )
-            assert(diff_result.returncode == 0), "Got unexpected return code {}".format(diff_result.returncode)
+            assert diff_result.returncode == 0, \
+                "Got unexpected return code {}".format(diff_result.returncode)
             for diff_line in diff_result.stdout.decode('utf-8').splitlines():
                 # don't skip test if there are any changes outside schemes
-                if not(diff_line.startswith('crypto_kem')) and not (diff_line.startswith('crypto_sign')):
-                    logging.info("Running all tests as there are changes outside of schemes")
+                if (not diff_line.startswith('crypto_kem') and
+                        not diff_line.startswith('crypto_sign')):
+                    logging.info("Running all tests as there are changes "
+                                 "outside of schemes")
                     return True
                 # do test if the scheme in question has been changed
                 if diff_line.startswith(thing.path(base='')):

test/test_duplicate_consistency.py

@@ -9,7 +9,7 @@ import unittest
 import yaml
 
 
-def skipped_test(*args, **kwargs):
+def _skipped_test(*args, **kwargs):
     raise unittest.SkipTest("Skipped consistency check")
 
 
@@ -18,7 +18,7 @@ def test_duplicate_consistency():
         for implementation in scheme.implementations:
             if not helpers.permit_test('duplicate_consistency',
                                        implementation):
-                yield skipped_test, implementation
+                yield _skipped_test, implementation
                 continue
 
             if os.path.isfile(