test: cover empty compatibility method returns

tests/test_validate_typecheck_diagnostics.py

@@ -108,6 +108,12 @@ class ValidateTypecheckDiagnosticsTests(unittest.TestCase):
     def test_includes_empty_function_return_fixture(self):
         self.assertIn("tests/typecheck_function_empty_return_bad.claro", MODULE.EXPECTED)
 
+    def test_includes_empty_compatibility_method_return_fixture(self):
+        self.assertIn(
+            "tests/typecheck_method_compat_empty_return_bad.claro",
+            MODULE.EXPECTED,
+        )
+
     def test_includes_missing_method_return_fixture(self):
         self.assertIn("tests/typecheck_method_missing_return_bad.claro", MODULE.EXPECTED)
 

tests/typecheck_method_compat_empty_return_bad.claro

@@ -0,0 +1,5 @@
+CLASS Player
+    TEACH score TAKES amount RETURNS NUMBER
+        RETURN
+    LEARNED
+ENDCLASS