Proposal: Add Eq instance for Control.Exception.ErrorCall

Michael Snoyman michael at
Tue Nov 27 13:25:32 CET 2012

On Tue, Nov 27, 2012 at 2:22 PM, Henning Thielemann <
lemming at> wrote:

> On Tue, 27 Nov 2012, Michael Snoyman wrote:
>  Sure, in some cases that's true. The idea would be to structure the test
>> case in such a way that we no with
>> certainty which way it will fail. Simon's initial example will always
>> fail in the same way.
> The message for head of empty list may be changed without warning ...

That argument can be applied to any form of automated testing.

doSomething :: Int -> Int

doSomething 5 `shouldBe` 6

If the behavior of doSomething suddenly changes, then your test will fail.
In fact, that's one of the *advantages* of having a test suite: it catches
these kinds of unexpected changes.

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