Use pathlib in relative path computation

haas/plugins/discoverer.py

@@ -8,6 +8,7 @@
 
 from fnmatch import fnmatch
 from importlib import import_module
+from pathlib import Path
 import logging
 import os
 import sys
@@ -41,10 +42,11 @@ def test_error(self):
 
 
 def get_relpath(top_level_directory, fullpath):
-    normalized = os.path.normpath(fullpath)
+    top_level = Path(top_level_directory).resolve()
+    normalized = Path(fullpath).resolve()
     logger.debug('Determine if %r is within %r',
-                 normalized, top_level_directory)
-    relpath = os.path.relpath(normalized, top_level_directory)
+                 str(normalized), str(top_level_directory))
+    relpath = str(normalized.relative_to(top_level))
     logger.debug('Relative path is %r', relpath)
     if os.path.isabs(relpath) or relpath.startswith('..'):
         raise ValueError('Path not within project: {0}'.format(fullpath))

haas/tests/test_haas_application.py

@@ -380,9 +380,7 @@ def test_multiple_start_directories(self, runner_class, result_class,
         try:
             fixture.create(tempdir)
 
-            from pathlib import Path
-
-            top_level = str(Path(os.path.join(tempdir, fixture.name)).resolve())
+            top_level = os.path.join(tempdir, fixture.name)
 
             # When
             with cd(top_level):