sonic-pi

https://github.com/sonic-pi-net/sonic-pi

C++

Code. Music. Live.

ActiveSupport::Testing::Assertions#assert_difference

Test numeric difference between the return value of an expression as a
result of what is evaluated in the yielded block.

  assert_difference 'Article.count' do
    post :create, article: {...}
  end

An arbitrary expression is passed in and evaluated.

  assert_difference 'assigns(:article).comments(:reload).size' do
    post :create, comment: {...}
  end

An arbitrary positive or negative difference can be specified.
The default is <tt>1</tt>.

  assert_difference 'Article.count', -1 do
    post :delete, id: ...
  end

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

  assert_difference [ 'Article.count', 'Post.count' ], 2 do
    post :create, article: {...}
  end

A lambda or a list of lambdas can be passed in and evaluated:

  assert_difference ->{ Article.count }, 2 do
    post :create, article: {...}
  end

  assert_difference [->{ Article.count }, ->{ Post.count }], 2 do
    post :create, article: {...}
  end

An error message can be specified.

  assert_difference 'Article.count', -1, 'An Article should be destroyed' do
    post :delete, id: ...
  end

Source | Google | Stack overflow

Edit

git clone [email protected]:sonic-pi-net/sonic-pi.git
cd sonic-pi
open app/server/ruby/vendor/activesupport-7.0.6/lib/active_support/testing/assertions.rb

Contribute

# Make a new branch
git checkout -b -your-name--update-docs-ActiveSupport--Testing--Assertions-assert_difference-for-pr

# Commit to git
git add app/server/ruby/vendor/activesupport-7.0.6/lib/active_support/testing/assertions.rbgit commit -m "better docs for ActiveSupport::Testing::Assertions#assert_difference"

# Open pull request
gem install hub # on a mac you can `brew install hub`
hub fork
git push <your name> -your-name--update-docs-ActiveSupport--Testing--Assertions-assert_difference-for-pr
hub pull-request

# Celebrate!