/ Ruby on Rails
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method

assert_no_difference

rails latest stable - Class: ActiveSupport::Testing::Assertions
assert_no_difference(expression, message = nil, &block)
public

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

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

A lambda can be passed in and evaluated.

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

An error message can be specified.

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

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

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

1Note

Takes array

eric_programmer ยท Jul 2, 2010

Like assert_difference this method can take an array of expressions to evaluate all of them. For example:

assert_no_difference ['Publisher.count', 'User.count', 'Membership.count'] do post :create end

It creates an assertion for each item in the array. So this will add three assertions to your test.