add test for backhandler

types/react-native/test/index.tsx

@@ -17,6 +17,7 @@ import {
     AppState,
     AppStateIOS,
     BackAndroid,
+    BackHandler,
     Button,
     DataSourceAssetCallback,
     DeviceEventEmitterStatic,
@@ -73,6 +74,8 @@ function testDimensions() {
     Dimensions.removeEventListener('change', dimensionsListener);
 }
 
+BackHandler.addEventListener("hardwareBackPress", () => {}).remove();
+
 BackAndroid.addEventListener("hardwareBackPress", () => {});
 
 interface LocalStyles {