Unit tests - create shareable mocks

[wise-king-sullyman]

Currently, mocks for our components have to be recreated in every unit test file where they're needed.

Component mocks that can be shared between all of our unit test files would make it easier to create new tests and make our tests more maintainable by removing code which otherwise needs to be repeated in multiple test files.

Mocks to create:

• Create shareable Button mock #8275