Fix tests

Author: afshin

.github/workflows/python-windows.yml

@@ -44,7 +44,12 @@ jobs:
         pip check
     - name: Run the tests
       run: |
-        pytest -vv
+        # Disable capturing (-s) output from Pytest on Windows.
+        # For an unknown reason, capturing output interferes with
+        # the file descriptions opened by the asyncio IOLoop.
+        # This leads to a nasty, flaky race condition that we haven't
+        # been able to solve.
+        pytest -vv -s
     - name: Install the Python dependencies for the examples
       run: |
         cd examples/simple && pip install -e .

jupyter_server/traittypes.py

@@ -228,11 +228,12 @@ def _resolve_classes(self):
         self.importable_klasses = []
         for klass in self.klasses:
             if isinstance(klass, str):
+                # Try importing the classes to compare. Silently, ignore if not importable.
                 try:
                     klass = self._resolve_string(klass)
                     self.importable_klasses.append(klass)
                 except:
-                    warn(f"{klass} is not importable. Is it installed?", ImportWarning)
+                    pass
             else:
                 self.importable_klasses.append(klass)
 
@@ -328,11 +329,12 @@ def _resolve_classes(self):
         self.importable_klasses = []
         for klass in self.klasses:
             if isinstance(klass, str):
+                # Try importing the classes to compare. Silently, ignore if not importable.
                 try:
                     klass = self._resolve_string(klass)
                     self.importable_klasses.append(klass)
                 except:
-                    warn(f"{klass} is not importable. Is it installed?", ImportWarning)
+                    pass
             else:
                 self.importable_klasses.append(klass)