assert_differences new syntax example

new_syntax_example.rb

assert_differences(['User.count', 'Post.count'], by: [-1, -5]) do
  # Logic...
end

assert_differences('User.count', by: -1) do
  # Logic... (although you should be using assert_difference in this case)
end

assert_differences(-> { User.count }, by: -1) do
  # I can do lambdas too!
end

assert_differences('User.count', by: -5, message: 'No can do, kiddo') do
  # Logic which shows your message on failure
end