Rspec #initialize behavior

gistfile1.rb

# Arbitrary class illustrating desired implementation of init options for a class
# How do I spec this behavior? especially if there are many attrs and conditions?

class Foo

  attr_accessor :bar

  def initialize(bar)
    # call an exiting method unless some condition is met by the variable passed in. Foo is an outward-facing class
    log_and_fail unless bar
    @bar = bar
  end

  def log_and_fail
    Log.fatal "fail" ; exit
  end

end