Add test, clarify reason for inline check

Author: kycutler

ipykernel/compiler.py

@@ -55,7 +55,7 @@ def _convert_to_long_pathname(filename):
                 filename = buf.value
             return filename
 
-        # test that it works
+        # test that it works so if there are any issues we fail just once here
         _convert_to_long_pathname(__file__)
     except:
         pass

ipykernel/tests/test_debugger.py

@@ -271,3 +271,9 @@ def test_rich_inspect_at_breakpoint(kernel_with_debug):
     )
 
     assert reply["body"]["data"] == {"text/plain": locals_[0]["value"]}
+
+
+def test_convert_to_long_pathname():
+    if sys.platform == 'win32':
+        from ipykernel.compiler import _convert_to_long_pathname
+        _convert_to_long_pathname(__file__)