instance method `assert_difference`

Ruby on Rails 8.0.4

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, *args, &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, params: { article: {...} }
end

An arbitrary expression is passed in and evaluated.

assert_difference 'Article.last.comments(:reload).size' do
  post :create, params: { comment: {...} }
end

An arbitrary positive or negative difference can be specified. The default is 1.

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

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

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

A hash of expressions/numeric differences can also be passed in and evaluated.

assert_difference ->{ Article.count } => 1, ->{ Notification.count } => 2 do
  post :create, params: { article: {...} }
end

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

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

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

An error message can be specified.

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

Parameters

expression req
args rest
block block

Source

# File activesupport/lib/active_support/testing/assertions.rb, line 101
      def assert_difference(expression, *args, &block)
        expressions =
          if expression.is_a?(Hash)
            message = args[0]
            expression
          else
            difference = args[0] || 1
            message = args[1]
            Array(expression).index_with(difference)
          end

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

        retval = _assert_nothing_raised_or_warn("assert_difference", &block)

        expressions.zip(exps, before) do |(code, diff), exp, before_value|
          actual = exp.call
          rich_message = -> do
            code_string = code.respond_to?(:call) ? _callable_to_source_string(code) : code
            error = "`#{code_string}` didn't change by #{diff}, but by #{actual - before_value}"
            error = "#{message}.\n#{error}" if message
            error
          end
          assert_equal(before_value + diff, actual, rich_message)
        end

        retval
      end

Defined in activesupport/lib/active_support/testing/assertions.rb line 101 · View on GitHub · Improve this page · Find usages on GitHub

Defined in ActiveSupport::Testing::Assertions

Signature

Parameters