diff --git a/android/filegroup.go b/android/filegroup.go
index fd4a2fe..3d1bbc5 100644
--- a/android/filegroup.go
+++ b/android/filegroup.go
@@ -23,7 +23,7 @@
 
 func init() {
 	RegisterModuleType("filegroup", FileGroupFactory)
-	RegisterBp2BuildMutator("filegroup", bp2buildMutator)
+	RegisterBp2BuildMutator("filegroup", FilegroupBp2Build)
 }
 
 // https://docs.bazel.build/versions/master/be/general.html#filegroup
@@ -51,7 +51,7 @@
 func (bfg *bazelFilegroup) GenerateAndroidBuildActions(ctx ModuleContext) {}
 
 // TODO: Create helper functions to avoid this boilerplate.
-func bp2buildMutator(ctx TopDownMutatorContext) {
+func FilegroupBp2Build(ctx TopDownMutatorContext) {
 	if m, ok := ctx.Module().(*fileGroup); ok {
 		name := "__bp2build__" + m.base().BaseModuleName()
 		ctx.CreateModule(BazelFileGroupFactory, &bazelFilegroupAttributes{
diff --git a/android/testing.go b/android/testing.go
index 76172d1..5640c29 100644
--- a/android/testing.go
+++ b/android/testing.go
@@ -89,7 +89,7 @@
 	f := func(ctx RegisterMutatorsContext) {
 		ctx.TopDown(mutatorName, m)
 	}
-	bp2buildMutators = append(bp2buildMutators, f)
+	ctx.bp2buildMutators = append(ctx.bp2buildMutators, f)
 }
 
 func (ctx *TestContext) Register() {
@@ -100,7 +100,7 @@
 
 // RegisterForBazelConversion prepares a test context for bp2build conversion.
 func (ctx *TestContext) RegisterForBazelConversion() {
-	RegisterMutatorsForBazelConversion(ctx.Context.Context, bp2buildMutators)
+	RegisterMutatorsForBazelConversion(ctx.Context.Context, ctx.bp2buildMutators)
 }
 
 func (ctx *TestContext) ParseFileList(rootDir string, filePaths []string) (deps []string, errs []error) {