We usually use SimpleLogger in tests, and some other binding when running in production.
In some cases, our tests depend on log values logged through the logger during a test.
Unfortunately between version 1.7.0 and 1.7.1 this ability has been removed, since the SimpleLogger now caches the system stream in a static initialiser.
Here is the code that broke this approach:
https://github.com/qos-ch/slf4j/commit/996ccc7ca507994465c069554954ecb01890d4d5

Basically, we would write a test:
{{
PrintStream err = System.err;
PrintStream temp = new PrintStream(some buffer here);
System.err = temp;
// run tests

System.err = err;
// here we assert that the temp stream contains values we expect}}

Unfortunately SimpleLogger now caches the system stream and never releases it, meaning swapping the streams to catch the output is not possible.