test: cover compatibility method addition returns

tests/test_validate_typecheck_diagnostics.py

@@ -116,6 +116,12 @@ class ValidateTypecheckDiagnosticsTests(unittest.TestCase):
             MODULE.EXPECTED_OK,
         )
 
+    def test_includes_compatibility_method_addition_return_success_fixture(self):
+        self.assertIn(
+            "tests/typecheck_method_compat_return_addition_good.claro",
+            MODULE.EXPECTED_OK,
+        )
+
     def test_includes_lowercase_compatibility_method_return_success_fixture(self):
         self.assertIn(
             "tests/typecheck_method_compat_lowercase_return_good.claro",

tests/typecheck_method_compat_return_addition_good.claro

@@ -0,0 +1,9 @@
+CLASS Player
+    TEACH score TAKES amount RETURNS NUMBER
+        CHECK TYPE amount IS NUMBER
+        RETURN amount + 2
+    LEARNED
+ENDCLASS
+
+NEW Player player
+CALL player.score WITH 4