Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / web / core / modules / simpletest / tests / modules / simpletest_test / simpletest_test.info.yml

name: 'Simpletest test'
type: module
description: 'Support module for Simpletest tests.'
package: Testing
version: VERSION
core: 8.x
dependencies:
  - drupal:entity_test