From: Dave Baldwin <dave.baldwin@3dlabs.com>
Date: 2007-07-13T17:55:01+09:00
Subject: Unit testing exception types and messages

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.