typecheck: diagnose missing declared returns

tests/test_validate_typecheck_diagnostics.py

@@ -44,6 +44,9 @@ class ValidateTypecheckDiagnosticsTests(unittest.TestCase):
         self.assertIn("tests/typecheck_function_return_bad.claro", MODULE.EXPECTED)
         self.assertIn("tests/typecheck_function_return_good.claro", MODULE.EXPECTED_OK)
 
+    def test_includes_missing_function_return_fixture(self):
+        self.assertIn("tests/typecheck_function_missing_return_bad.claro", MODULE.EXPECTED)
+
 
 if __name__ == "__main__":
     unittest.main()

tests/typecheck_function_missing_return_bad.claro

@@ -0,0 +1,5 @@
+TEACH square amount RETURNS NUMBER
+    SAY amount
+END
+
+DO square 4