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comp.lang.ruby

Unit testing exception types and messages

Dave Baldwin

7/13/2007 8:55:00 AM

Testing that an exception of the given type is raised is easy with
assert_raise:

assert_raise(SomeExceptoin) {raise SomeExceptoin, "some message"}

but if I want to also test the exception message how do I do this?
My first though was to try:

assert_raise(SomeExceptoin) {raise SomeExceptoin, "some message"}
assert_equal( "some message", $!.message)

relying on $! to hold the information message from the last raise,
but this doesn't work as assert_raise sets $! to nil somewhere along
the line.

I can use an idiom like:

begin
raise SomeExceptoin, "some message"
rescue
assert_equal("some message", $!.message)
assert_raise(SomeExceptoin) {raise SomeExceptoin, "some message"}
end

in the tests, but this isn't very DRY. This could be improved by
inventing a assert_raise_with_message method to hide this, but is
there a way already defined in the unit testing framework to handle
this?

Thanks,

Dave.
1 Answer

gabriele renzi

7/13/2007 9:47:00 AM

0

On Fri, 13 Jul 2007 17:55:01 +0900, Dave Baldwin wrote:

<snip>
I do not think that there is a builtin assertion for exception
messages, but defining your assert_raise_message is easy[1].
But I thought I'd point out a small detail:

> I can use an idiom like:
>
> begin
> raise SomeExceptoin, "some message"
> rescue
> assert_equal("some message", $!.message)
> assert_raise(SomeExceptoin) {raise SomeExceptoin, "some message"}
> end

this seem slightly wrong, wouldn't it be
begin
# raise SomeException with "some message"
rescue => e
assert_equal("some message", e.message)
assert_instance_of SomeException, e
end
?
perlish variables are ugly and I think there is no need to raise the
exception again.


[1]
even but I'd like to have a simple way to have filter_backtrace hide my own
custom assertions



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