test(button-dropdown): add testcase

tests/utils.ts

@@ -1,3 +1,9 @@
 export const sleep = (time: number) => {
   return new Promise(resolve => setTimeout(resolve, time))
 }
+
+export const mockNativeEvent = (fn: Function = () => {}) => ({
+  nativeEvent: { stopImmediatePropagation: fn }
+})
+
+export const nativeEvent = mockNativeEvent()