Updates the test cases to use thunderfx

[kiya00]

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

As a follow-up of #1529 , this PR updates the test cases to use new interface thunderfx

[mruberry]

Cool!

Maybe in the future we should support using thunderfx as a decorator, like @thunderfx(...), too, but that's not urgent