package: Add diagnostic to check if a package is the latest version

Closes: #2148.

Tests:

- For an app with older version of package installed, run diagnostics. A warning
is shown. Latest version available is shown correctly in the message.

- For an app with latest version of package installed, run diagnostics. Test
shows as passed.

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

plinth/package.py

@@ -78,6 +78,27 @@ class Packages(app.FollowerComponent):
         helper = module.setup_helper
         helper.install(self.packages, skip_recommends=self.skip_recommends)
 
+    def diagnose(self):
+        """Run diagnostics and return results."""
+        results = super().diagnose()
+        cache = apt.Cache()
+        for package_name in self.packages:
+            result = 'warning'
+            latest_version = '?'
+            if package_name in cache:
+                package = cache[package_name]
+                latest_version = package.candidate.version
+                if package.candidate.is_installed:
+                    result = 'passed'
+
+            message = _('Package {package_name} is the latest version '
+                        '({latest_version})').format(
+                            package_name=package_name,
+                            latest_version=latest_version)
+            results.append([message, result])
+
+        return results
+
     def find_conflicts(self) -> Optional[list[str]]:
         """Return list of conflicting packages installed on the system."""
         if not self.conflicts:

plinth/tests/test_package.py

@@ -60,6 +60,24 @@ def test_packages_setup():
         [call(['foo2', 'bar2'], skip_recommends=True)])
 
 
+@patch('apt.Cache')
+def test_diagnose(cache):
+    """Test checking for latest version of the package."""
+    cache.return_value = {
+        'package2': Mock(candidate=Mock(version='2.0', is_installed=True)),
+        'package3': Mock(candidate=Mock(version='3.0', is_installed=False)),
+    }
+    component = Packages('test-component',
+                         ['package1', 'package2', 'package3'])
+    results = component.diagnose()
+    assert '(?)' in results[0][0]
+    assert results[0][1] == 'warning'
+    assert '(2.0)' in results[1][0]
+    assert results[1][1] == 'passed'
+    assert '(3.0)' in results[2][0]
+    assert results[2][1] == 'warning'
+
+
 @patch('plinth.package.packages_installed')
 def test_packages_find_conflicts(packages_installed_):
     """Test finding conflicts."""