1 files changed, 20 insertions, 0 deletions
diff --git a/src/test/java/org/shedlang/compiler/types/TypeSubstitutionTests.java b/src/test/java/org/shedlang/compiler/types/TypeSubstitutionTests.java
index 8bca5f3f..37341a7a 100644
--- a/src/test/java/org/shedlang/compiler/types/TypeSubstitutionTests.java
+++ b/src/test/java/org/shedlang/compiler/types/TypeSubstitutionTests.java
@@ -42,6 +42,26 @@ public class TypeSubstitutionTests {
     }
 
     @Test
+    public void substitutingEffectUnionUpdatesMembersOfUnion() {
+        var effect1 = Effects.userDefined(NAMESPACE_NAME, "Effect1");
+        var effect2 = Effects.userDefined(NAMESPACE_NAME, "Effect2");
+        var typeSubstitutionMap = TypeSubstitutionMap.of(
+            Map.entry(EffectParam.forStructType(STRUCT_TYPE, "E1"), effect1),
+            Map.entry(EffectParam.forStructType(STRUCT_TYPE, "E2"), effect2)
+        );
+
+        var result = TypeSubstitution.substituteEffect(
+            Effects.union(
+                EffectParam.forStructType(STRUCT_TYPE, "E1"),
+                EffectParam.forStructType(STRUCT_TYPE, "E2")
+            ),
+            typeSubstitutionMap
+        );
+
+        assertThat(result, equalTo(Effects.union(effect1, effect2)));
+    }
+
+    @Test
     public void substitutingEffectIoDoesNothing() {
         var typeSubstitutionMap = TypeSubstitutionMap.of(
             Map.entry(EffectParam.forStructType(STRUCT_TYPE, "E"), Effects.NONE)