instance method `assert_changes`

Ruby on Rails 8.1.2

Since v5.2.8.1

Available in: 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_changes(expression, message = nil, from: UNTRACKED, to: UNTRACKED, &block)

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. The comparison is done using case equality (===), which means you can specify patterns or classes:

# Exact value match
assert_changes :@object, from: nil, to: :foo do
  @object = :foo
end

# Case equality
assert_changes -> { user.token }, to: /\w{32}/ do
  user.generate_token
end

# Type check
assert_changes -> { current_error }, from: nil, to: RuntimeError do
  raise "Oops"
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

Parameters

expression req
message opt = nil
from key = UNTRACKED
to key = UNTRACKED
block block

Source

# File activesupport/lib/active_support/testing/assertions.rb, line 212
      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
          rich_message = -> do
            error = "Expected change from #{from.inspect}, got #{before.inspect}"
            error = "#{message}.\n#{error}" if message
            error
          end
          assert from === before, rich_message
        end

        after = exp.call

        rich_message = -> do
          code_string = expression.respond_to?(:call) ? _callable_to_source_string(expression) : expression
          error = "`#{code_string}` didn't change"
          error = "#{error}. It was already #{to.inspect}." if before == to
          error = "#{message}.\n#{error}" if message
          error
        end
        refute_equal before, after, rich_message

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

        retval
      end

Defined in activesupport/lib/active_support/testing/assertions.rb line 212 · View on GitHub · Improve this page · Find usages on GitHub

Defined in ActiveSupport::Testing::Assertions

Signature

Parameters