Add a test that actually checks the vendored schema against upstream.

tests/system_tests/test_schema.py

@@ -0,0 +1,19 @@
+import contextlib
+import io
+import unittest
+
+from debugger_protocol.schema.__main__ import handle_check
+
+
+class VendoredSchemaTests(unittest.TestCase):
+
+    def test_matches_upstream(self):
+        stdout = io.StringIO()
+        with contextlib.redirect_stdout(stdout):
+            with contextlib.redirect_stderr(stdout):
+                try:
+                    handle_check()
+                except Exception as exc:
+                    self.fail(str(exc))
+        result = stdout.getvalue().strip().splitlines()[-1]
+        self.assertEqual(result, 'schema file okay')