Monkey patching sucks.

But this makes this stuff at least testable.

src/rs500common/configuration.py

@@ -1,6 +1,6 @@
 import configparser
 from os import getenv
-from os.path import join, exists, isfile
+import os.path
 from pathlib import Path
 
 
@@ -17,19 +17,19 @@ class ConfigProvider(object):
 
 def discover_config_file_by_name(filename: str, script_dir: str=None, env_var: str='RS500_CONFIG_PATH') -> str:
     if script_dir is not None:
-        candidate = join(script_dir, filename)
-        if exists(candidate) and isfile(candidate):
+        candidate = os.path.join(script_dir, filename)
+        if os.path.exists(candidate) and os.path.isfile(candidate):
             return candidate
     if env_var is not None:
         env_var_value = getenv(env_var, None)
         if env_var_value is not None:
-            candidate = join(env_var_value, filename)
-            if exists(candidate) and isfile(candidate):
+            candidate = os.path.join(env_var_value, filename)
+            if os.path.exists(candidate) and os.path.isfile(candidate):
                 return candidate
-    candidate = join(str(Path.home().absolute()), '.rs500', filename)
-    if exists(candidate) and isfile(candidate):
+    candidate = os.path.join(str(Path.home().absolute()), '.rs500', filename)
+    if os.path.exists(candidate) and os.path.isfile(candidate):
         return candidate
-    candidate = join('/etc', filename)
-    if exists(candidate) and isfile(candidate):
+    candidate = os.path.join('/etc', filename)
+    if os.path.exists(candidate) and os.path.isfile(candidate):
         return candidate
     raise FileNotFoundError('Unable to find configuration file "{}"'.format(filename))

src/test/test_configuration_file_discovery.py

@@ -1,4 +1,4 @@
-import os
+import os.path
 
 import pytest
 from _pytest.monkeypatch import MonkeyPatch
@@ -7,11 +7,9 @@ from rs500common.configuration import discover_config_file_by_name
 
 
 def test_discovery(monkeypatch: MonkeyPatch):
-    def mock(path):
-        return True
     with monkeypatch.context() as m:
-        m.setattr(os.path, 'isfile', mock)
-        m.setattr(os.path, 'exists', mock)
+        m.setattr('os.path.isfile', lambda path: True)
+        m.setattr('os.path.exists', lambda path: True)
         result = discover_config_file_by_name('test.ini', '/foo/bar')
     assert result == os.path.join('/foo/bar', 'test.ini')