Groundwork for Studio extensibility

Implement a Studio tab plugin manager, define a namespace for Studio tab plugins, and introduce an abstract base class used to represent Studio tabs. This does not introduce changes required to inject such plugins into the Studio UI. ECOM-2187.

cms/lib/tests/test_studio_tabs.py

@@ -0,0 +1,35 @@
+"""Tests for the Studio tab plugin API."""
+from django.test import TestCase
+import mock
+
+from cms.lib.studio_tabs import StudioTabPluginManager
+from openedx.core.lib.api.plugins import PluginError
+
+
+class TestStudioTabPluginApi(TestCase):
+    """Unit tests for the Studio tab plugin API."""
+
+    @mock.patch('cms.lib.studio_tabs.StudioTabPluginManager.get_available_plugins')
+    def test_get_enabled_tabs(self, get_available_plugins):
+        """Verify that only enabled tabs are retrieved."""
+        enabled_tab = self._mock_tab(is_enabled=True)
+        mock_tabs = {
+            'disabled_tab': self._mock_tab(),
+            'enabled_tab': enabled_tab,
+        }
+
+        get_available_plugins.return_value = mock_tabs
+
+        self.assertEqual(StudioTabPluginManager.get_enabled_tabs(), [enabled_tab])
+
+    def test_get_invalid_plugin(self):
+        """Verify that get_plugin fails when an invalid plugin is requested."""
+        with self.assertRaises(PluginError):
+            StudioTabPluginManager.get_plugin('invalid_tab')
+
+    def _mock_tab(self, is_enabled=False):
+        """Generate a mock tab."""
+        tab = mock.Mock()
+        tab.is_enabled = mock.Mock(return_value=is_enabled)
+
+        return tab