I probably have quite a fundamentalist view on unit testing because I write primarily in purely functional code these days - where a "unit" is a pure function, and it's clearly an isolated unit. Even when I'm back in OOP world though, I basically avoid static variables/globals like the plague. Even where the framework or some library makes use of them, I'll tend to wrap them up and pass them into my code via Main, to make sure that no statics are globally accessible throughout the code.

If I were testing a salary calculation which takes values from a database, and I named my test "Test_salary_calculation_correct", where instead of using some sample data which could easily cover the range of values I need to test against, I instead relied on a database connection, and this test failed because the database was not accessible - I've only confused the developer who picks up my shit where "Test_salary_calculation_correct" fails, and he thinks there's a problem with my calculation rather than a misconfigured firewall somewhere else. The firewall has nothing to do with my salary calcuation - why should it have any effect on the test passing?

The way I see unit tests is this: If you write a test and it passes on your machine, then some other developer takes your code and the same test fails - it's a fuckup on your behalf. Unit tests should not depend on the environment in any way. Actually, by definition, a unit test is a test of a single "unit" - including database access into this is well beyond the scope of unit testing, but into integration testing.

To me it seems you're skipping unit testing and just going onto integration testing with your unit testing framework. I'm not sure what you've observed or where, but I can tell you it's certainly not standard or best practice in the industry. It might possibly tell you something about your own code style though - are you writing units which can be treated in isolation? (Certainly not if you depend on a SL, which is a global context of services with no clear boundary)

Ideally a codebase should be designed to maximize unit-testability and reduce the need for integration testing to as little as possible - since this is where most of the "unexpected", or "out of my control" problems are most likely to occur. This testing is more a case of "am I handling all the relevant exceptions" than getting green lights to pass in a unit testing framework. It doesn't really help to make unit tests against code which is expected to fail out in the wild due to whatever circumstance - what matters here is that your code is prepared for the worst and knows how to recover.

It's these cases where mock classes are particularly useful - because you can forcefully simluate any behavior from the external service and make sure your code is working correctly for all the potential circumstances. Having to rely on divine intervention to trigger some event that may only happen 1% of the time in the real-world situation is hardly practical. Unfortunately testing in the wild is often like this - everything works fine 99% of the time.

Even for cases where you're arguing for a fixture with real test data in (from a database), then the reasonable thing to do is extract this data beforehand and encode it into the unit testing language (which is fairly trivial to do). Now you have a reliable test which will continue to work as you update the code. Testing against live data is giving a false sense of security to begin with anyway. Imagine the scenario where you have a bunch of data in the database, you run your unit test against it with all green flags - then after deployment, somebody inserts into the database a value which your code doesn't expect. The unit test shouldn't be testing against real world data, but against data representitive of the possible values it should accept (ie, include all the obvious edge cases which should fail too, but are not likely to exist in the real world DB).