Fix (?) tests that I think should error

Hi @d11, I am not sure here: can you explain why these 5 tests
were not expected to error? I am almost sure that they should 
throw an error, since E != D and M != D. In the upcoming new parsing
of the dimensions, it does error.

We might have a mismatch in our two expectations of the function's behaviour :)
Can we check that when I come back on Tuesday, please?
Refactor mvn.rnd in case of result tensor

The generated systematic tests pass :)
I am not sure if I should review the case without result tensor: I
haven't touched it.