def assert_difference(expressions, difference = 1, message = nil, &block)
expression_evaluations = Array(expressions).map do |expression|
[expression, lambda do
eval(expression, block.__send__(:binding))
end]
end
original_values = expression_evaluations.inject([]) { |memo, expression| memo << expression[1].call }
yield
expression_evaluations.each_with_index do |expression, i|
full_message = ""
full_message << "#{message}.\n" if message
full_message << "<#{expression[0]}> was the expression that failed"
assert_equal original_values[i] + difference, expression[1].call, full_message
end
end