carolineartz
2/28/2014 - 3:57 AM

From http://stackoverflow.com/questions/21353945/is-there-a-way-to-test-argument-errors-from-within-a-method-to-return-true-or-fa

From http://stackoverflow.com/questions/21353945/is-there-a-way-to-test-argument-errors-from-within-a-method-to-return-true-or-fa

test-argument-errors.rb
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class Die
  def initialize(sides)
    @sides=sides
    unless @sides>0
      raise ArgumentError.new("Your number sucks, yo")
      # As per the doc you could write the above line as below also
      # raise ArgumentError, "Your number sucks, yo"
    end
  end

  #returns the number of sides of a die
  def sides
    @sides
  end

  #generates a random die roll based on the number of sides
  def roll
    rand(@sides)+1
  end
end

Die.new(0) rescue $!.message == "Your number sucks, yo"
# => true

#above can also be written 
begin
  Die.new(0)
rescue ArgumentError => e
  bad = e.message
end 
bad == "Your number sucks, yo" # => true
Notes.md
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####From the documentation of Exception

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.

So once I have just raised exception in the $! global variable, I can use Exception#message method, which returns the exception’s message or name.

####You use Kernel#raise

With no arguments, raises the exception in $! or raises a RuntimeError if $! is nil. With a single String argument, raises a RuntimeError with the string as a message. Otherwise, the first parameter should be the name of an Exception class (or an object that returns an Exception object when sent an exception message). The optional second parameter sets the message associated with the exception, and the third parameter is an array of callback information. Exceptions are caught by the rescue clause of begin...end blocks.