Ruby: How do I return a boolean value if the correct error is raised?

ruby, testing

Solution

When an exception has been raised but not yet handled (in rescue, ensure, at_exit and END blocks) the global variable $! will contain the current exception and $@ contains the current exception’s backtrace.

Do as below (using inline `rescue` way):

2.0.0-p0 :001 > [1, 2, 3].first("two")
TypeError: no implicit conversion of String into Integer
    from (irb):1:in 'first'
    from (irb):1
    from /home/kirti/.rvm/rubies/ruby-2.0.0-p0/bin/irb:16:in '<main>'
2.0.0-p0 :002 > [1, 2, 3].first("two") rescue $!.class == TypeError
 => true 
2.0.0-p0 :003 > [1, 2, 3]['a'] rescue $!.class == TypeError
 => true 
2.0.0-p0 :004 > [1, 2, 3]['a']
TypeError: no implicit conversion of String into Integer
    from (irb):4:in '[]'
    from (irb):4
    from /home/kirti/.rvm/rubies/ruby-2.0.0-p0/bin/irb:16:in '<main>'
2.0.0-p0 :005 > 1/0 rescue $!.class == TypeError
 => false 
2.0.0-p0 :006 >

`TypeError`

Raised when encountering an object that is not of the expected type.

[1, 2, 3].first("two")

raises the exception: TypeError: no implicit conversion of String into Integer

In your case you could write as below :

some_method(arg) rescue $!.class == TypeError

Problem

I'm interested in comparing if the correct errors are raised for my code. If the correct error is raised then it returns true, otherwise false. Is there a way to go about it? Or would I need to write exception handling? For example, ``` some_method(arg) == TypeError # => true ```

Original source