class ActiveSupport::TestCase

def assert_nothing_raised(*args)

end
...
assert_nothing_raised do

Fails if the block raises an exception. 
def assert_nothing_raised(*args)
  yield
end

def test_order

Defaults to +:sorted+.
Possible values are +:random+, +:parallel+, +:alpha+, +:sorted+.

ActiveSupport::TestCase.test_order # => :sorted

Returns the order in which test cases are run. 
def test_order
  test_order = ActiveSupport.test_order
  if test_order.nil?
    ActiveSupport::Deprecation.warn "You did not specify a value for the " \
      "configuration option `active_support.test_order`. In Rails 5, " \
      "the default value of this option will change from `:sorted` to " \
      "`:random`.\n" \
      "To disable this warning and keep the current behavior, you can add " \
      "the following line to your `config/environments/test.rb`:\n" \
      "\n" \
      "  Rails.application.configure do\n" \
      "    config.active_support.test_order = :sorted\n" \
      "  end\n" \
      "\n" \
      "Alternatively, you can opt into the future behavior by setting this " \
      "option to `:random`."
    test_order = :sorted
    self.test_order = test_order
  end
  test_order
end

def test_order=(new_order)

* +:alpha+ (equivalent to +:sorted+)
* +:sorted+ (to run tests alphabetically by method name)
* +:parallel+ (to run tests in parallel)
* +:random+ (to run tests in random order)
Valid values are:

ActiveSupport::TestCase.test_order = :random # => :random

Sets the order in which test cases are run. 
def test_order=(new_order)
  ActiveSupport.test_order = new_order
end