Ayende @ Rahien

It's a girl

Find the issue

There is a design issue that is revealed in the following tests, can you figure out why I changed the behavior and removed the tests?

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Comments

Ryan Schipper
07/11/2010 07:52 AM by
Ryan Schipper

A couple of things that need consideration in my opinion.

1) in my opinion it is inappropriate to force your API consumer to use exception handlers for normal process flow as demonstrated in the first few tests

2) a dictionary is a reasonably established paradigm and standard practice (at least where I come from) would suggest that the add function should be add(key, value). Instead, you have an explicitly required container class.

One of these may even be what you are thinking of..

Anon
07/11/2010 08:32 AM by
Anon

Issue is very simple. I am annoyed with you because you have not posted anything for 9 days. I hope all is well, but I'm annoyed anyway.

Kristof Claes
07/11/2010 09:05 AM by
Kristof Claes

Did it have something to do with the fact that before you add an item, you have to check if it already exists or not and trying to get an unregistered item throws an exeption?

Thomas Eyde
07/11/2010 11:52 AM by
Thomas Eyde

You found out that you wanted a set, not a dictionary?

More specifically, deleting a non existing item can be considered already deleted, adding an existing item can be considered as an overwrite, and retrieving a non existing item could return null.

I am not sure about the last one, but add and delete in this fashion should not throw.

fschwiet
07/11/2010 05:31 PM by
fschwiet

Just yesterday I hit a bug where within one session I read an item (discarding the result) then wrote an item with the same key. This caused an exception, as would be expected by the last test. I would've preferred it would just overwrite. I assumed I was doing it wrong, maybe that will change.

The design problem may be that adding an item may throw an exception (if it has same key as existing), while the only way the caller can check if that will happen (by loading whatever has that key) could also throw an exception. So any typical use then involves handling an exception.

Just feedback on the last test... Its better to only have the one line that will throw an exception within the Assert.Throws() expression. Otherwise this test may pass for the wrong reason when an earlier line fails inappropriately.

Rik Hemsley
07/11/2010 05:51 PM by
Rik Hemsley

Going by what I see in the tests, ApplicationInstanceDictionary is no different from Dictionary <guid,> , so you should use the .NET class and this means you don't need to test it.

Kevin McCormick
07/11/2010 07:32 PM by
Kevin McCormick

Since this collection is tied to the class, the guid/key restrictions are kind of unnecessary. The dictionary class should manage duplicates, keys, etc. internally, and you should be able to manipulate the collection via index, linq, and provide indexing by guid only as an added bonus (ie, myColl.FindByGuid() ) if it's really necessary.

Rik Hemsley
07/11/2010 08:52 PM by
Rik Hemsley

When I said Dictionary, the blog software ate my angle brackets, because it's rubbish (it still fails to 'remember me' despite offering to). So I meant a dictionary of Guid => string.

Steve Py
07/12/2010 01:29 AM by
Steve Py

If ApplicationInstanceDictionary extends Dictionary, then it would appear that you are testing the default behaviour of a Dictionary, though the types of exceptions thrown might be different.

Andrey Titov
07/12/2010 05:34 AM by
Andrey Titov

You changed them to TryRemove, TryAdd and TryGet to support concurrency?

Martin O'Keefe
07/12/2010 08:04 AM by
Martin O'Keefe

'ApplicationInstance'

You need to maintain references to the GUID keys - the keys are required by consumers of values.

I would have suggested making the key the Type, but you are passing two strings as values - that's out.

I'm assuming that you chose GUID because the values are not user configurable - otherwise const string keys would appear to be better.

If the key is to be dynamic it seems that you need to make the key deterministic based on the type and its scope etc.

Frank Quednau
07/12/2010 05:54 PM by
Frank Quednau

Just from the API perspective I don't like the asymmetry of adding ApplicationInstances and removing Guids.

Jon Norton
07/12/2010 08:59 PM by
Jon Norton

In CannotAddDuplicatedItems() the test could pass due to an InvalidOperationException being thown before the last Add where the test is actually expecting the exception to be thrown. The Arrange portion of the test is included in the Action and Assert section represented by the Assert.Throws.

meo
07/13/2010 02:50 PM by
meo

TMM, it is strange design, when you have 'firstInstance' != 'secondInstance' due to same key and different values in it (in 3rd test), but adding second after the first one will fail with InvalidOperation. It's inconsistent

meisinger
07/15/2010 05:11 PM by
meisinger

the exception type is wrong

either that or you have determined that writing unit tests are silly and not needed

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