Hi Christoph,


> On Apr 9, 2020, at 7:01 AM, Thiede, Christoph <Christoph.Thiede at student.hpi.uni-potsdam.de> wrote:
> 
> 
> Hi all,
> 
> 
> 
> please take a short look at this behavior:
> 
> 
> 
> TestRunner openForSuite: MorphicUIManagerTest suite. "Run Selected"
> 
> 
> At the moment (#19541), a bug in FileList2 class >> #endingSpecs (which I'm going to fix ASAP) breaks the test #testShowAllBinParts. But because ModificationForbidden is not an Error, it is not caught by the TestRunner so the whole suite run blows up, too.
> I could make another example by triggering a ModificationForbidden in a #drawOn: method to destroy the whole image, too.
> (Morph newSubclass compile: 'drawOn: x #(1) at: 1 put: 2'; new) openInHand)
> 
> So my question is: Why doesn't ModificationForbidden derive from Error? Isn't it actually an error? Similar illegal operations such as "#() at: 0" or "{} at: 1 put: #foo" raise some kind of Error, too. Everything I learned so far about Squeak's exception framework tells me that you should have a very good reason if you design an exception neither to derive from Error, nor from Notification. At the moment, we only do have 9 exceptions (bad pun ...) to this rule (and I'm not even sure whether MCNoChangesException couldn't be a notification, and Abort does not even have senders in the Trunk).
> I'd be happy if you could give me some pointers on why ModificationForbidden does not follow this rule. How can we deal with this in order to fix the bugs/unexpected behaviors mentioned above?

I think this is an oversight in my part.  I agree that ModificationForbidden is an error.  I took the code from Pharo and didn’t notice ModificationForbidden was a Notification.

Please feel free to make it an Error.

> 
> Possibly related stuff:
> http://forum.world.st/Squeak-s-AssertionFailure-vs-SUnit-s-TestFailure-td5106818.html
> http://forum.world.st/The-Trunk-Kernel-eem-1294-mcz-td5112196.html
> http://forum.world.st/The-Trunk-Kernel-eem-1317-mcz-tp5113273p5113433.html
> 
> Best,
> Christoph
> 
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