Use mockito-scala-scalatest to enable strict mocks on all tests.

[ultrasecreth]

Inspired by the comment on #172 this PR uses the ScalaTest integration of mockito-scala so all mocks are strict by default.

An easy way to verify this would be to re-write the first test on LoggerSpec as (notice the extra direct call to underlying.info

    "call the underlying logger's error method if the error level is enabled" in {
        val f = fixture(_.isErrorEnabled, isEnabled = true)
        import f._
        logger.error(msg)
        underlying.info("called by accident")
        verify(underlying).error(msg)
    }

Executing such test would fail as

Unexpected invocations found

The following invocations are unexpected (click to navigate to relevant line of code):
1. logger.info("called by accident"); -> at com.typesafe.scalalogging.LoggerSpec.$anonfun$new$2(LoggerSpec.scala:26)
Please make sure you aren't missing any stubbing or that your code actually does what you want
org.mockito.exceptions.misusing.UnexpectedInvocationException: Unexpected invocations found

This change has already paid by itself as it shown that the tests on LoggerWithTaggedArgsSpec L#68 and L#77 were not testing anything as the wrong log level was being enabled

[ultrasecreth]

Strict mode also means that if you stub something and is not used you'll get a failure as it indicates your code is not doing what the test expected it to do, hence the flag to only stub this for the tests that do a positive verification

[ultrasecreth]

Had to add the verification due to strict-mode (if a mock method is called, and it wasn't either stubbed nor verified the test will fail)
I had to add the 3rd param as the macro always calls the varargs version of the Slf4j class, but on the direct call to verify, the compiler would pick the overloaded non-vararg version and the verification would fail as they are effectively different methods. By using 3 arguments the problem goes away as the only option is the varargs method

[ultrasecreth]

This test and the next were actually not testing anything, as the incorrect log level was being enabled, thanks strict mode!! :)

[SethTisue]

I don't know anything about Mockito... is there anyone watching this repo who can review this?

(If we can't find anybody, I guess I'll merge regardless after a waiting period...)