Need to mark config as dirty in _handle_migrations()

Add tests for tabs.persist_mode_on_change migration

qutebrowser/config/configfiles.py

@@ -179,14 +179,13 @@ class YamlConfig(QObject):
             elif name in configdata.MIGRATIONS.deleted:
                 log.config.debug("Removing {}".format(name))
                 del self._values[name]
-
         persist = 'tabs.persist_mode_on_change'
         if persist in self._values:
             if self._values[persist]:
                 self._values['tabs.mode_on_change'] = 'persist'
             else:
                 self._values['tabs.mode_on_change'] = 'normal'
-            del self._values[persist]
+            self.unset(persist)
 
     def _validate(self):
         """Make sure all settings exist."""

tests/unit/config/test_configfiles.py

@@ -169,6 +169,30 @@ class TestYaml:
         assert '  old:' not in lines
         assert '  new:' not in lines
 
+    def test_merge_persist_false(self, monkeypatch, yaml, config_tmpdir):
+        """Migration of tabs.persist_mode_on_change: False."""
+        autoconfig = config_tmpdir / 'autoconfig.yml'
+        autoconfig.write_text('global:\n  tabs.persist_mode_on_change: False', encoding='utf-8')
+
+        yaml.load()
+        yaml._save()
+
+        lines = autoconfig.read_text('utf-8').splitlines()
+        assert '  tabs.persist_mode_on_change:' not in lines
+        assert '  tabs.mode_on_change: normal' in lines
+
+    def test_merge_persist_true(self, monkeypatch, yaml, config_tmpdir):
+        """Migration of tabs.persist_mode_on_change: True."""
+        autoconfig = config_tmpdir / 'autoconfig.yml'
+        autoconfig.write_text('global:\n  tabs.persist_mode_on_change: True', encoding='utf-8')
+
+        yaml.load()
+        yaml._save()
+
+        lines = autoconfig.read_text('utf-8').splitlines()
+        assert '  tabs.persist_mode_on_change:' not in lines
+        assert '  tabs.mode_on_change: persist' in lines
+
     def test_renamed_key_unknown_target(self, monkeypatch, yaml,
                                         config_tmpdir):
         """A key marked as renamed with invalid name should raise an error."""