Unit testing exception types and messages

Ruby
1

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.

2

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

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

3

e = assert_raise(RuntimeError) { my_code_that_raises }
assert_match(/Error message here/i, e.message)

Jason