add unit test and fix issues with it

qutebrowser/config/configfiles.py

@@ -85,6 +85,7 @@ class YamlConfig:
         self._filename = os.path.join(standarddir.config(auto=True),
                                       'autoconfig.yml')
         self.values = {}
+        self._initial_values = {}
 
     def init_save_manager(self, save_manager):
         """Make sure the config gets saved properly.
@@ -119,7 +120,7 @@ class YamlConfig:
             with open(self._filename, 'r', encoding='utf-8') as f:
                 yaml_data = utils.yaml_load(f)
         except FileNotFoundError:
-            return
+            return {}
         except OSError as e:
             desc = configexc.ConfigErrorDesc("While reading", e)
             raise configexc.ConfigFileErrors('autoconfig.yml', [desc])

tests/unit/config/test_configfiles.py

@@ -72,16 +72,17 @@ def test_yaml_config(fake_save_manager, config_tmpdir, old_config, insert):
 
     yaml._save()
 
-    text = autoconfig.read_text('utf-8')
+    if not insert and old_config is None:
-    lines = text.splitlines()
+        lines = []
-    print(lines)
-
-    assert lines[0].startswith('# DO NOT edit this file by hand,')
-    assert 'config_version: {}'.format(yaml.VERSION) in lines
-
-    if old_config is None and not insert:
-        assert 'global: {}' in lines
     else:
+        text = autoconfig.read_text('utf-8')
+        lines = text.splitlines()
+        print(lines)
+
+        if insert:
+            assert lines[0].startswith('# DO NOT edit this file by hand,')
+            assert 'config_version: {}'.format(yaml.VERSION) in lines
+
         assert 'global:' in lines
 
     # WORKAROUND for https://github.com/PyCQA/pylint/issues/574
@@ -91,6 +92,27 @@ def test_yaml_config(fake_save_manager, config_tmpdir, old_config, insert):
         assert '  tabs.show: never' in lines
 
 
+@pytest.mark.parametrize('old_config', [
+    None,
+    'global:\n  colors.hints.fg: magenta',
+])
+def test_yaml_config_unchanged(fake_save_manager, config_tmpdir, old_config):
+    autoconfig = config_tmpdir / 'autoconfig.yml'
+    mtime = None
+    if old_config is not None:
+        autoconfig.write_text(old_config, 'utf-8')
+        mtime = autoconfig.stat().mtime
+
+    yaml = configfiles.YamlConfig()
+    yaml.load()
+    yaml._save()
+
+    if old_config is None:
+        assert not autoconfig.exists()
+    else:
+        assert autoconfig.stat().mtime == mtime
+
+
 @pytest.mark.parametrize('line, text, exception', [
     ('%', 'While parsing', 'while scanning a directive'),
     ('global: 42', 'While loading data', "'global' object is not a dict"),