Warning, long post. I accidentally run the dev version of moose on a 2.0 to check if the VMs work properly and I ran into a bunch of failing tests. https://ci.inria.fr/pharo/view/3.0-VM/job/PharoVM-AcceptanceTest/27/SLAVE=ph... First of all, my problem, since I wanted to test the #stable release anyway. In any case I had a look at the bugs since I was interested to see if it was in any way VM-related: https://ci.inria.fr/pharo/view/3.0-VM/job/PharoVM-AcceptanceTest/27/SLAVE=ph... Ok, 0 information :(, why? Because of #shouldnt:raise:. On a linguistic basis the #shouldnt:raise: message makes sense, sort of the counter part of #should:raise:... BUT how does it handle errors exactly? Example 1: ---------- self shouldnt: [ 1 doeSomething ] raise: MessageNotUnderstood. ok, seems fine, the test should fail, most probably with an assertion failure, and this is what it does indeed. Example 2: ---------- self shouldnt: [ 1/0 ] raise: MessageNotUnderstood. will that now fail or not? Because it doesn't raise the MessageNotUnderstood, so the logic conclusion is that it doesn't fail. Well, you're wrong, it WILL FAIL, with a ZeroDivide, which is the major reason #shouldnt:raise: is not helpful. That is utterly confusing and rather useless. Because you can just write 1 doeSomething. 1/0. - In case 1 you get an MessageNotUnderstood instead of an AssertionFailure => test fails in both cases - In the second case you get the same message, so nothing to discuss about. The interesting part is, that case 1 almost never happens like I've shown it. Most of the time it looks more like this (including the failing moose tests): self shouldnt: [ 1 doeSomething ] raise: Error. This is in my eye useless, even worse, it is obstructing, since you basically mute an otherwise useful error. In the original example, I was left with no stack trace nor a decent reason why the test would fail. Whereas with a bit of stack trace I would get reasonable context to start real debugging efforts. Conclusion: ----------- a) do not use #shouldnt:raise: b) still don't use it c) if you want to use #shouldnt:raise: for dubious reasons, use very specific errors you test for, othew