module ActiveSupport::Testing::Assertions

end
post :create, params: { article: invalid_attributes }
assert_no_difference [ 'Article.count', -> { Post.count } ] do

An array of expressions can also be passed in and evaluated.

end
post :create, params: { article: invalid_attributes }
assert_no_difference 'Article.count', 'An Article should not be created' do

An error message can be specified.

end
post :create, params: { article: invalid_attributes }
assert_no_difference -> { Article.count } do

A lambda can be passed in and evaluated.

end
post :create, params: { article: invalid_attributes }
assert_no_difference 'Article.count' do

changed before and after invoking the passed in block.
Assertion that the numeric result of evaluating an expression is not

def assert_no_difference(expression, message = nil, &block)
  assert_difference expression, 0, message, &block
end