We already implemented PaymentHandler on Android much but there are no enough tests.
It causes many problems such as a crash and something. To ship this feature as soon as possible, we should write more tests and put efforts into them.

Especially, we should write the following tests preferentially:
  1. PaymentHandler Brower Tests on Android.
     Current test implementation can not install actual service worker.
     So, we should change the structure, and then write more tests such as triggering event.
  2. Content side tests
     In this layer, there are some tests but it's so basic. We should be able to cover edge cases.
  3. web-platform-tests
     If possible, we should write much tests via this way.
     Then, it can be matched up with spec and other browser vendors.