Flowdock
method

assert_difference

Importance_2
assert_difference(expression, difference = 1, message = nil, &block) public

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 +1.

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 error message can be specified.

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