test: Test case for extended SpriteButtonComponent

[puneet-739]

Description

Added an extra test case for testing SpriteButtonComponent class.
which includes a CustomSpriteButtonComponet class to test the working with onLoad instead of directly using Constructor.

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Related Issues

It may help working on the issues like #3293

[spydon]

Tests for the SpriteButtonComponent should live in the sprite_button_component_test.dart file.

[puneet-739]

Tests for the SpriteButtonComponent should live in the sprite_button_component_test.dart file.

done

[spydon]

These tests are just copies of already existing tests, but going through an extended version that isn't exposed to the user. I don't think we want this type of testing pattern in the code-base.
If you disagree with a good argument I can open it again, but I'll close it for now.

[puneet-739]

These tests are just copies of already existing tests, but going through an extended version that isn't exposed to the user. I don't think we want this type of testing pattern in the code-base. If you disagree with a good argument I can open it again, but I'll close it for now.

Oh, ok.
Actually, I've added the test cases due to the issue #3293. (I think there is still an issue) Please refer to this comment #3302 (comment)
The reason of adding the test cases is to test the working of SpriteButtonComponent with extended version. because the issue #3293 only occurs when the user use the extended version but not on the Constructor.
So, we need to test if the issue is resolved for the extended version as well, as the present test cases only test for Constructor version, it will always give positive result (it gives error if we use the extended version).

[spydon]

@puneet-739 you're right, can you try #3327? It should solve the issue so that the user doesn't have to call super.onLoad last.
EDIT: Needs another fix, working on it now.

[spydon]

@puneet-739 I changed my mind, due to the intricacies of the SpriteButtonComponent it's probably good to have these tests so that we don't get any regressions later. Can you fix the DCM warning? (Make the CustomSpriteButtonComponent private)