Test subtype as free type param

1 files changed, 21 insertions, 0 deletions

diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java
index 5f7fede9..33e47ff8 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java
@@ -189,6 +189,27 @@ public class TypeCheckerIsSubTypeTests {
         assertThat(error.actual(), equalTo(Types.INT));
     }
 
+    @Test
+    public void whenSubtypeIsFreeTypeParamThenOtherTypesAreNotSupertype() {
+        var typeParam = TypeParam.forStructType(
+            Types.struct(NamespaceName.of("Example"), "Struct"),
+            "T"
+        );
+
+        var error = assertThrows(
+            UnexpectedTypeError.class,
+            () -> TypeCheckerSubTyping.addSubtypeConstraint(
+                typeParam,
+                Types.INT,
+                Sources.NULL,
+                TypeCheckerSubTyping.constraints(List.of(), TypeInfos.EMPTY)
+            )
+        );
+
+        assertThat(error.expected(), equalTo(TypeSets.type(Types.INT)));
+        assertThat(error.actual(), equalTo(typeParam));
+    }
+
     // == Sum types ==
 
     @Test