diff --git a/android/transition_test.go b/android/transition_test.go
new file mode 100644
index 0000000..f7618f3
--- /dev/null
+++ b/android/transition_test.go
@@ -0,0 +1,162 @@
+// Copyright 2024 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package android
+
+import "testing"
+
+type testTransitionMutator struct {
+	split              func(ctx BaseModuleContext) []string
+	outgoingTransition func(ctx OutgoingTransitionContext, sourceVariation string) string
+	incomingTransition func(ctx IncomingTransitionContext, incomingVariation string) string
+	mutate             func(ctx BottomUpMutatorContext, variation string)
+}
+
+func (t *testTransitionMutator) Split(ctx BaseModuleContext) []string {
+	if t.split != nil {
+		return t.split(ctx)
+	}
+	return []string{""}
+}
+
+func (t *testTransitionMutator) OutgoingTransition(ctx OutgoingTransitionContext, sourceVariation string) string {
+	if t.outgoingTransition != nil {
+		return t.outgoingTransition(ctx, sourceVariation)
+	}
+	return sourceVariation
+}
+
+func (t *testTransitionMutator) IncomingTransition(ctx IncomingTransitionContext, incomingVariation string) string {
+	if t.incomingTransition != nil {
+		return t.incomingTransition(ctx, incomingVariation)
+	}
+	return incomingVariation
+}
+
+func (t *testTransitionMutator) Mutate(ctx BottomUpMutatorContext, variation string) {
+	if t.mutate != nil {
+		t.mutate(ctx, variation)
+	}
+}
+
+func TestModuleString(t *testing.T) {
+	bp := `
+		test {
+			name: "foo",
+		}
+	`
+
+	var moduleStrings []string
+
+	GroupFixturePreparers(
+		FixtureRegisterWithContext(func(ctx RegistrationContext) {
+
+			ctx.PreArchMutators(func(ctx RegisterMutatorsContext) {
+				ctx.Transition("pre_arch", &testTransitionMutator{
+					split: func(ctx BaseModuleContext) []string {
+						moduleStrings = append(moduleStrings, ctx.Module().String())
+						return []string{"a", "b"}
+					},
+				})
+			})
+
+			ctx.PreDepsMutators(func(ctx RegisterMutatorsContext) {
+				ctx.Transition("pre_deps", &testTransitionMutator{
+					split: func(ctx BaseModuleContext) []string {
+						moduleStrings = append(moduleStrings, ctx.Module().String())
+						return []string{"c", "d"}
+					},
+				})
+			})
+
+			ctx.PostDepsMutators(func(ctx RegisterMutatorsContext) {
+				ctx.Transition("post_deps", &testTransitionMutator{
+					split: func(ctx BaseModuleContext) []string {
+						moduleStrings = append(moduleStrings, ctx.Module().String())
+						return []string{"e", "f"}
+					},
+					outgoingTransition: func(ctx OutgoingTransitionContext, sourceVariation string) string {
+						return ""
+					},
+				})
+				ctx.BottomUp("rename_bottom_up", func(ctx BottomUpMutatorContext) {
+					moduleStrings = append(moduleStrings, ctx.Module().String())
+					ctx.Rename(ctx.Module().base().Name() + "_renamed1")
+				}).UsesRename()
+				ctx.BottomUp("final", func(ctx BottomUpMutatorContext) {
+					moduleStrings = append(moduleStrings, ctx.Module().String())
+				})
+			})
+
+			ctx.RegisterModuleType("test", mutatorTestModuleFactory)
+		}),
+		FixtureWithRootAndroidBp(bp),
+	).RunTest(t)
+
+	want := []string{
+		// Initial name.
+		"foo{}",
+
+		// After pre_arch (reversed because rename_top_down is TopDown so it visits in reverse order).
+		"foo{pre_arch:b}",
+		"foo{pre_arch:a}",
+
+		// After pre_deps (reversed because post_deps TransitionMutator.Split is TopDown).
+		"foo{pre_arch:b,pre_deps:d}",
+		"foo{pre_arch:b,pre_deps:c}",
+		"foo{pre_arch:a,pre_deps:d}",
+		"foo{pre_arch:a,pre_deps:c}",
+
+		// After post_deps.
+		"foo{pre_arch:a,pre_deps:c,post_deps:e}",
+		"foo{pre_arch:a,pre_deps:c,post_deps:f}",
+		"foo{pre_arch:a,pre_deps:d,post_deps:e}",
+		"foo{pre_arch:a,pre_deps:d,post_deps:f}",
+		"foo{pre_arch:b,pre_deps:c,post_deps:e}",
+		"foo{pre_arch:b,pre_deps:c,post_deps:f}",
+		"foo{pre_arch:b,pre_deps:d,post_deps:e}",
+		"foo{pre_arch:b,pre_deps:d,post_deps:f}",
+
+		// After rename_bottom_up.
+		"foo_renamed1{pre_arch:a,pre_deps:c,post_deps:e}",
+		"foo_renamed1{pre_arch:a,pre_deps:c,post_deps:f}",
+		"foo_renamed1{pre_arch:a,pre_deps:d,post_deps:e}",
+		"foo_renamed1{pre_arch:a,pre_deps:d,post_deps:f}",
+		"foo_renamed1{pre_arch:b,pre_deps:c,post_deps:e}",
+		"foo_renamed1{pre_arch:b,pre_deps:c,post_deps:f}",
+		"foo_renamed1{pre_arch:b,pre_deps:d,post_deps:e}",
+		"foo_renamed1{pre_arch:b,pre_deps:d,post_deps:f}",
+	}
+
+	AssertDeepEquals(t, "module String() values", want, moduleStrings)
+}
+
+func TestTransitionMutatorInFinalDeps(t *testing.T) {
+	GroupFixturePreparers(
+		FixtureRegisterWithContext(func(ctx RegistrationContext) {
+			ctx.FinalDepsMutators(func(ctx RegisterMutatorsContext) {
+				ctx.Transition("vars", &testTransitionMutator{
+					split: func(ctx BaseModuleContext) []string {
+						return []string{"a", "b"}
+					},
+				})
+			})
+
+			ctx.RegisterModuleType("test", mutatorTestModuleFactory)
+		}),
+		FixtureWithRootAndroidBp(`test {name: "foo"}`),
+	).
+		ExtendWithErrorHandler(FixtureExpectsOneErrorPattern("not allowed in FinalDepsMutators")).
+		RunTest(t)
+}