app: Introduce API to run diagnostics on an app

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

plinth/app.py

@@ -104,6 +104,24 @@ class App:
             if not component.is_leader:
                 component.set_enabled(enabled)
 
+    def diagnose(self):
+        """Run diagnostics and return results.
+
+        Return value must be a list of results. Each result is a two-tuple with
+        first value as user visible description of the test followed by the
+        result. The test result is a string enumeration from 'failed', 'passed'
+        and 'error'.
+
+        Results are typically collected by diagnosing each component of the app
+        and then supplementing the results with any app level diagnostic tests.
+
+        """
+        results = []
+        for component in self.components.values():
+            results.extend(component.diagnose())
+
+        return results
+
 
 class Component:
     """Interface for an app component."""
@@ -121,6 +139,17 @@ class Component:
         """Run operations to enable the component."""
     def disable(self):
         """Run operations to disable the component."""
+    @staticmethod
+    def diagnose():
+        """Run diagnostics and return results.
+
+        Return value must be a list of results. Each result is a two-tuple with
+        first value as user visible description of the test followed by the
+        result. The test result is a string enumeration from 'failed', 'passed'
+        and 'error'.
+
+        """
+        return []
 
 
 class FollowerComponent(Component):

plinth/tests/test_app.py

@@ -34,6 +34,10 @@ class LeaderTest(FollowerComponent):
     """Test class for using LeaderComponent in tests."""
     is_leader = True
 
+    def diagnose(self):
+        """Return diagnostic results."""
+        return [('test-result-' + self.component_id, 'success')]
+
 
 @pytest.fixture(name='app_with_components')
 def fixture_app_with_components():
@@ -182,6 +186,13 @@ def test_app_set_enabled(app_with_components):
     assert app.components['test-leader-1'].is_enabled()
 
 
+def test_app_diagnose(app_with_components):
+    """Test running diagnostics on an app."""
+    results = app_with_components.diagnose()
+    assert results == [('test-result-test-leader-1', 'success'),
+                       ('test-result-test-leader-2', 'success')]
+
+
 def test_component_initialization():
     """Test that component is initialized properly."""
     with pytest.raises(ValueError):
@@ -192,6 +203,12 @@ def test_component_initialization():
     assert not component.is_leader
 
 
+def test_component_diagnose():
+    """Test running diagnostics on component."""
+    component = Component('test-component')
+    assert component.diagnose() == []
+
+
 def test_follower_component_initialization():
     """Test that follower component is initialized properly."""
     component = FollowerComponent('test-follower-1')