instance method `assert_difference`

Ruby on Rails 4.2.9

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 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

Parameters

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

Source

# File activesupport/lib/active_support/testing/assertions.rb, line 63
      def assert_difference(expression, difference = 1, message = nil, &block)
        expressions = Array(expression)

        exps = expressions.map { |e|
          e.respond_to?(:call) ? e : lambda { eval(e, block.binding) }
        }
        before = exps.map { |e| e.call }

        yield

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

Defined in activesupport/lib/active_support/testing/assertions.rb line 63 · View on GitHub · Improve this page · Find usages on GitHub

Defined in ActiveSupport::Testing::Assertions

Signature

Parameters