From: Eric Hodel <drbrain@...7.net>
Date: 2006-03-09T07:57:47+09:00
Subject: Re: assert_raise question

On Mar 8, 2006, at 1:42 PM, Sean Carley wrote:

> Currently, assert_raise expects you to know exactly what kind of  
> exception
> is going to be thrown by raise.  Basically it tests to see if  
> exception.class ==
> expected.class.
>
> I think a more appropriate behavior would be to test  
> exception.kind_of?expected.  I would also be happy if there were  
> one method that performed the way it does currently and another  
> that checks exception parentage.

For a given input a method should only raise one class of exception.   
The restriction forces you to write better tests.

> Please see the code below for an example of two tests.  I think  
> both should
> pass but only the first test does because ArgumentError !=  
> StandardError.

require 'socket'
require 'test/unit'

class MyClass
   def connect(overthere)
     unless overthere =~ /:\d+\Z/ then
       raise ArgumentError, "Use host:port, got #{overthere}"
     end
     host, port = overthere.split ':'
     @socket = TCPSocket.new host, port.to_i
   end
end

This method can raise at least two different exceptions on bad input  
so you should test for them separately.  This allows consumers of  
your code to behave properly depending upon what arguments they feed  
your code.

class TestMyClass < Test::Unit::TestCase

   def setup
     @obj = MyClass.new
   end

   def test_connect_bad_args_no_port
     assert_raises ArgumentError do
       @obj.connect 'host'
     end
   end

   def test_connect_bad_args_bad_port
     assert_raises ArgumentError do
       @obj.connect 'host:port'
     end
   end

   def test_connect_bad_host
     assert_raises SocketError do
       @obj.connect 'no-such-host.example.com:80'
     end
   end

end

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant

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