expressionの結果が変化したかどうかを検証するassertion

assert_change.rb

def assert_change(expression, message = nil, &block)
  exp = expression.respond_to?(:call) ? expression : ->{ eval(expression, block.binding) }
  before = exp.call
  yield
  error = "#{expression.inspect} didn't change"
  error = "#{message}.\n#{error}" if message
  assert_not_equal before, exp.call, error
end

def assert_not_change(expression, message = nil, &block)
  exp = expression.respond_to?(:call) ? expression : ->{ eval(expression, block.binding) }
  before = exp.call
  yield
  error = "#{expression.inspect} changed"
  error = "#{message}.\n#{error}" if message
  assert_equal before, exp.call, error
end