inheritance_diagram: Move _import_class_or_module() method to function

tests/roots/test-ext-inheritance_diagram/example/__init__.py

@@ -0,0 +1 @@
+# example.py

tests/roots/test-ext-inheritance_diagram/example/sphinx.py

@@ -0,0 +1,5 @@
+# example.sphinx
+
+
+class DummyClass(object):
+    pass

tests/test_ext_inheritance_diagram.py

@@ -9,9 +9,54 @@
     :license: BSD, see LICENSE for details.
 """
 
-from util import with_app
+import sys
+from util import with_app, rootdir, raises
+from sphinx.ext.inheritance_diagram import InheritanceException, import_classes
 
 
 @with_app('html', testroot='ext-inheritance_diagram')
 def test_inheritance_diagram_html(app, status, warning):
     app.builder.build_all()
+
+
+def test_import_classes():
+    from sphinx.application import Sphinx, TemplateBridge
+
+    try:
+        sys.path.append(rootdir / 'roots/test-ext-inheritance_diagram')
+
+        # got exception for unknown class or module
+        raises(InheritanceException, import_classes, 'unknown', None)
+        raises(InheritanceException, import_classes, 'unknown.Unknown', None)
+
+        # a module having no classes
+        classes = import_classes('sphinx', None)
+        assert classes == []
+
+        classes = import_classes('sphinx', 'foo')
+        assert classes == []
+
+        # all of classes in the module
+        classes = import_classes('sphinx.application', None)
+        assert set(classes) == set([Sphinx, TemplateBridge])
+
+        # specified class in the module
+        classes = import_classes('sphinx.application.Sphinx', None)
+        assert classes == [Sphinx]
+
+        # specified class in current module
+        classes = import_classes('Sphinx', 'sphinx.application')
+        assert classes == [Sphinx]
+
+        # ignore current module if name include the module name
+        raises(InheritanceException, import_classes, 'i18n.CatalogInfo', 'sphinx.util')
+
+        # got exception for functions
+        raises(InheritanceException, import_classes, 'encode_uri', 'sphinx.util')
+
+        # try to load example.sphinx, but inheritance_diagram imports sphinx instead
+        # refs: #3164
+        classes = import_classes('sphinx', 'example')
+        assert classes == []
+    finally:
+        sys.path.pop()