Use arrange act assert pattern in tests

Merged Eric Bruneton requested to merge use-arrange-act-assert-pattern-in-tests into master

This only for the asm and asm-tree packages for now. I will do the other ones separately (this merge request is already very large). These other tests are refactored a bit because I changed ClassDump to ClassFile in asm-test, made it public, and removed the custom Assertions class. But they don't follow the arrange-act-assert pattern yet.

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