FakeLogger collects the log messages so you can later retrieve them, in a test.

I knew that collecting logs was handy especially in testing, maybe you will notice there's no much value on this PR, but I'm sure FakeLogger is much better than NullLogger because it give us the ability to collect the logs, that's why ASP.NET Core bring it in the latest version

while FakeLogger is unnecessary and potentially an impact on performance too

This is true if we use it in the code-base, but I used for testing ONLY

But we don't do anything with the logs. If we were, then FakeLogger would be useful. However, for the instances you changed, no logging is required, the mocks and NullLogger were only injected to not have the code break due to null references. So, using FakeLogger causes unnecessary overhead but brings no value.

I understand this is only about testing, but test execution performance matters too.

I will close this for now, but once when need the logs records on the testing FakeLogger is our choice :)

Then absolutely, just these are not such cases.