Introduce mock test base

[ArcturusZhang]

Prerequisite PR: #22524

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[pakrym]

The only purpose of this base class seems to be to diable instrumentation validation. Not worth having a class for that.

[ArcturusZhang]

And it turns out this overriding is also not needed.

I believe it is very possible that we could only use the MockTestEnvironment to indicate the test was a mock test.

@m-nash what do you think?

[pakrym]

You don't need a test environment for mock tests because they would never run live.

[ArcturusZhang]

That is true, but I need the Credential to be the mock credential even not in Playback mode

[pakrym]

Can you use new MockCredential()?