Generic way to test for expected SystemCallError

Ruby
1

Hi all,

Ruby 1.8.x

I’ve got a few tests where I’m looking for expected errors. These are
various system call errors. The problem is that the exact Errno is
different from platform to platform, so I end up writing stuff like
this:

assert_raises(Errno::EACCES, Errno::ENOTEMPTY){ Dir.unlink(‘some_dir’)
}

This isn’t very robust, since a new platform might fail with a
different kind of Errno. What I would like is a way to have this test
succeed:

assert_raises(SystemCallError){ Dir.unlink(‘some_dir’) }

The problem is that assert_raises looks for a specific error class. Is
there a way to tell TestUnit to expect any error that’s a subclass of
SystemCallError?

Thanks,

Dan

PS - I see from the documentation that assert_raise is deprecated in
1.9. What’s replacing it?

2

Daniel B. wrote:

}

Thanks,

Dan

PS - I see from the documentation that assert_raise is deprecated in
1.9. What’s replacing it?

The simplest way to do this which comes to my mind is to use the fact
that the
exceptions you need are the only constants in the Errno module. This
allows
you to write

assert_raise(*(Errno.constants.map{|c| Errno.const_get©}))
{Dir.unlink(‘some_dir’)}

Errno.constants gives you an array with the names of the constants,
which are
the names of the exception claesses you’re interested in. The map method
transforms the array of names in an array of classes, obtained using
Errno.const_get

As for assert_raises being deprecated, I think it’s simply a matter of
names,
since the method replacing it is simply assert_raise (without the final
s).

I hope this helps

Stefano

3

Stefano C. wrote:

assert_raises(Errno::EACCES, Errno::ENOTEMPTY){ Dir.unlink(‘some_dir’)
SystemCallError?
you to write

assert_raise(*(Errno.constants.map{|c| Errno.const_get©}))
{Dir.unlink(‘some_dir’)}

Errno.constants gives you an array with the names of the constants, which are
the names of the exception claesses you’re interested in. The map method
transforms the array of names in an array of classes, obtained using
Errno.const_get

Ugly, but I guess it will have to do. I’ll probably wrap that in its
own method. Perhaps I can convince Nathaniel to either add a
“assert_raise_kind_of” method, or allow assert_raise to take another
argument.

As for assert_raises being deprecated, I think it’s simply a matter of names,
since the method replacing it is simply assert_raise (without the final s).

Oh, I could have sworn they were both deprecated. Perhaps I was
looking at old docs. Disregard. I can’t wait to go through all of my
tests and update those. Not.

Thanks,

Dan

4

I had the same issue with TestUnit. I wound up writing my own
assert_raise function, which I named assert_raise_s, based on the
TestUnit assert_raise code. I then extend test/unit with the code.

require ‘test/unit’
require ‘assert_raise_s.rb’

I tried to attach the code but am getting a Rails Application Error.
Should I post the code itself?