[FEATURE] Add key to submit button for integration testing

[jalakoo]

Is your feature request related to a problem? Please describe.
Not a clear way to target the login/submit button to trigger in an integration test. There is a test util function for the packages own test, but as far as I can tell the animated_button widget is not accessible outside of the package.

Describe the solution you'd like
Would like to be able to something like tester.tap(find.byKey(Key("flutter_login_submit_button"); to trigger a tap on the submit button.

Additional context

[danhunsaker]

Similar problem. Our app requires login to reach anything beyond the home screen, and I can't actually automate the login process without some way to find the relevant elements, so I can't write integration tests at the moment.

Unless I'm just missing something in the docs?

[danhunsaker]

Not in the docs, but digging through the package code leads to a workaround.

import 'package:flutter_login/src/widgets/animated_button.dart';
import 'package:flutter_login/src/widgets/animated_text_form_field.dart';

.
.
.

      final name = find.byType(AnimatedTextFormField).first;
      final pass = find.byType(AnimatedPasswordTextFormField).first;
      final btn = find.byType(AnimatedButton).first;

      await tester.enterText(name, '5');
      await tester.enterText(pass, '5');

      await tester.press(btn);

Definitely a bit fragile, as it depends on implementation details we shouldn't know or care about. Which is why it would be better to have keys on everything instead.