package: Prevent freedombox's deps from removal during app uninstall

- If an app declares dependency on package that is also a dependency for
freedombox, then during the app's uninstall, the dependency is attempt to be
removed and will fail (because freedombox package will be held state).

- Add freedombox (and thus its dependencies) to the list packages that should be
removed from list of packages to be removed during app uninstall.

- In test case, update list of packages attempted removal as the 'freedombox'
package is installed only in some environments.

Tests:

- Uninstall janus works. Log messages show that libjs-bootstrap5 and
node-popper2 are in the list of packages originally set to removed during app
uninstall but are later filtered out.

- Run pytest with 'freedombox' package installed and ensure all tests pass.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/package.py

@@ -308,9 +308,9 @@ class Packages(app_module.FollowerComponent):
         """
         packages_set: set[str] = set(packages)
 
-        # Get list of packages needed by other installed apps (packages to
-        # keep).
-        keep_packages: set[str] = set()
+        # Get list of packages needed by other installed apps and by freedombox
+        # itself (packages to keep).
+        keep_packages: set[str] = {'freedombox'}
         for app in app_module.App.list():
             # uninstall() will be called on Packages of this app separately
             # for uninstalling this app.

plinth/tests/test_package.py

@@ -178,11 +178,11 @@ def test_packages_uninstall(uninstall, _refresh_package_lists):
         """Test app"""
         app_id = 'test-app'
 
-    component = Packages('test-component', ['python3', 'bash'])
+    component = Packages('test-component', ['bash', 'dash'])
     app = TestApp()
     app.add(component)
     app.uninstall()
-    uninstall.assert_has_calls([call(['python3', 'bash'], purge=True)])
+    uninstall.assert_has_calls([call(['bash', 'dash'], purge=True)])
 
 
 @patch('plinth.package.refresh_package_lists')