refresh your browser: I just edited the tests so that the calls and the assertions are now concomitant. That should be good. Improved a bit the error messages too.

warning, the tests are "rather shity", about that part: there are actually several tests, some with the exact same assertion message but testing different things. I'll bet you're not failing the same every time, depending on your changes. Try to carefully print all the data you have to track doown the thing. If not enough, I can past the inputs of the tests.

note: your class is called on 4 different inputs, and only then the 4 related assertions are made, so be very careful with what's happening...

should throw IllegalArgumentException if array is null

-> ?

(forget about the actual/expected part, it's not relevant, for those tests)