instance method `assert_difference`

Ruby on Rails 3.0.20

Since v2.3.18

Available in: v2.3.18 v3.0.20 v3.1.12 v3.2.22.5 v4.0.13 v4.1.16 v4.2.9 v5.2.8.1 v6.0.6 v6.1.7.10 v7.0.10 v7.1.6 v7.2.3 v8.0.4 v8.1.2

Compare with:

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

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

Parameters

expression req
difference opt = 1
message opt = nil
block block

Source

# File activesupport/lib/active_support/testing/assertions.rb, line 37
      def assert_difference(expression, difference = 1, message = nil, &block)
        b = block.send(:binding)
        exps = Array.wrap(expression)
        before = exps.map { |e| eval(e, b) }

        yield

        exps.each_with_index do |e, i|
          error = "#{e.inspect} didn't change by #{difference}"
          error = "#{message}.\n#{error}" if message
          assert_equal(before[i] + difference, eval(e, b), error)
        end
      end

Defined in activesupport/lib/active_support/testing/assertions.rb line 37 · View on GitHub · Improve this page · Find usages on GitHub

Defined in ActiveSupport::Testing::Assertions

Signature

Parameters