assert.rb

## Definition of assert!
class AssertError < RuntimeError; end
def assert!(&block)
  raise AssertError.new("Assertion failed!") if !block.call
rescue AssertError => e
  print e
  code = <<-CODE
    require 'pry'
    binding.pry
  CODE
  eval(code, block.binding)
  raise e
end

## example
assert!{ a == 3 }