diff --git a/java/testing.go b/java/testing.go
index 6c49bc8..82aa29b 100644
--- a/java/testing.go
+++ b/java/testing.go
@@ -146,6 +146,10 @@
 // This defines a file in the mock file system in a predefined location (prebuilts/sdk/Android.bp)
 // and so only one instance of this can be used in each fixture.
 func FixtureWithPrebuiltApis(release2Modules map[string][]string) android.FixturePreparer {
+	return FixtureWithPrebuiltApisAndExtensions(release2Modules, nil)
+}
+
+func FixtureWithPrebuiltApisAndExtensions(apiLevel2Modules map[string][]string, extensionLevel2Modules map[string][]string) android.FixturePreparer {
 	mockFS := android.MockFS{}
 	path := "prebuilts/sdk/Android.bp"
 
@@ -153,14 +157,20 @@
 			prebuilt_apis {
 				name: "sdk",
 				api_dirs: ["%s"],
+				extensions_dir: "extensions",
 				imports_sdk_version: "none",
 				imports_compile_dex: true,
 			}
-		`, strings.Join(android.SortedStringKeys(release2Modules), `", "`))
+		`, strings.Join(android.SortedStringKeys(apiLevel2Modules), `", "`))
 
-	for release, modules := range release2Modules {
+	for release, modules := range apiLevel2Modules {
 		mockFS.Merge(prebuiltApisFilesForModules([]string{release}, modules))
 	}
+	if extensionLevel2Modules != nil {
+		for release, modules := range extensionLevel2Modules {
+			mockFS.Merge(prebuiltExtensionApiFiles([]string{release}, modules))
+		}
+	}
 	return android.GroupFixturePreparers(
 		android.FixtureAddTextFile(path, bp),
 		android.FixtureMergeMockFs(mockFS),
@@ -198,6 +208,19 @@
 	return fs
 }
 
+func prebuiltExtensionApiFiles(extensionLevels []string, modules []string) map[string][]byte {
+	fs := make(map[string][]byte)
+	for _, level := range extensionLevels {
+		for _, sdkKind := range []android.SdkKind{android.SdkPublic, android.SdkSystem, android.SdkModule, android.SdkSystemServer} {
+			for _, lib := range modules {
+				fs[fmt.Sprintf("prebuilts/sdk/extensions/%s/%s/api/%s.txt", level, sdkKind, lib)] = nil
+				fs[fmt.Sprintf("prebuilts/sdk/extensions/%s/%s/api/%s-removed.txt", level, sdkKind, lib)] = nil
+			}
+		}
+	}
+	return fs
+}
+
 // FixtureConfigureBootJars configures the boot jars in both the dexpreopt.GlobalConfig and
 // Config.productVariables structs. As a side effect that enables dexpreopt.
 func FixtureConfigureBootJars(bootJars ...string) android.FixturePreparer {