return True on successful ExtensionPoint validation

and include validate() in test coverage, which fails prior to the change because validate() returned None

Author: minrk

jupyter_server/extension/manager.py

@@ -129,6 +129,8 @@ def validate(self):
             self._get_loader()
         except Exception:
             return False
+        else:
+            return True
 
     def link(self, serverapp):
         """Link the extension to a Jupyter ServerApp object.

jupyter_server/tests/extension/test_manager.py

@@ -30,6 +30,7 @@ def test_extension_point_api():
     assert app is not None
     assert callable(e.load)
     assert callable(e.link)
+    assert e.validate()
 
 
 def test_extension_point_metadata_error():
@@ -59,6 +60,7 @@ def test_extension_package_api():
     assert hasattr(e, "extension_points")
     assert len(e.extension_points) == len(metadata_list)
     assert app.name in e.extension_points
+    assert e.validate()
 
 
 def test_extension_package_notfound_error():