You should never mock anything. Test against the same dependencies that exist in production.
If that's impossible (i.e. you get charged for the backends or you are controlling physical objects), then generalize the program to support alternative backends and frequently test only those that can work in the test environment, using some more ad-hoc methodologies for the others.
Also, in general, if you need to change your tests for valid changes in the implementation, then your approach to testing is completely broken. An example are dumb testing strategies where you check that the code produces specific SQL queries instead of checking that the code returns correct results.
If that's impossible (i.e. you get charged for the backends or you are controlling physical objects), then generalize the program to support alternative backends and frequently test only those that can work in the test environment, using some more ad-hoc methodologies for the others.
Also, in general, if you need to change your tests for valid changes in the implementation, then your approach to testing is completely broken. An example are dumb testing strategies where you check that the code produces specific SQL queries instead of checking that the code returns correct results.