method

assert_changes

rails latest stable - Class: ActiveSupport::Testing::Assertions

assert_changes(expression, message = nil, from: UNTRACKED, to: UNTRACKED, &block)

public

Assertion that the result of evaluating an expression is changed before and after invoking the passed in block.

assert_changes 'Status.all_good?' do
  post :create, params: { status: { ok: false } }
end

You can pass the block as a string to be evaluated in the context of the block. A lambda can be passed for the block as well.

assert_changes -> { Status.all_good? } do
  post :create, params: { status: { ok: false } }
end

The assertion is useful to test side effects. The passed block can be anything that can be converted to string with #to_s.

assert_changes :@object do
  @object = 42
end

The keyword arguments :from and :to can be given to specify the expected initial value and the expected value after the block was executed.

assert_changes :@object, from: nil, to: :foo do
  @object = :foo
end

An error message can be specified.

assert_changes -> { Status.all_good? }, 'Expected the status to be bad' do
  post :create, params: { status: { incident: true } }
end

# File activesupport/lib/active_support/testing/assertions.rb, line 191
      def assert_changes(expression, message = nil, from: UNTRACKED, to: UNTRACKED, &block)
        exp = expression.respond_to?(:call) ? expression : -> { eval(expression.to_s, block.binding) }

        before = exp.call
        retval = _assert_nothing_raised_or_warn("assert_changes", &block)

        unless from == UNTRACKED
          error = "Expected change from #{from.inspect}, got #{before}"
          error = "#{message}.\n#{error}" if message
          assert from === before, error
        end

        after = exp.call

        error = "#{expression.inspect} didn't change"
        error = "#{error}. It was already #{to}" if before == to
        error = "#{message}.\n#{error}" if message
        refute_equal before, after, error

        unless to == UNTRACKED
          error = "Expected change to #{to}, got #{after}\n"
          error = "#{message}.\n#{error}" if message
          assert to === after, error
        end

        retval
      end

assert_changes

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