update validation message spec. it is enough for us to test that discussion fails validation because there is no user. no need to check for a rails error message that has changed from 4 -> 5
after_commit callbacks do not run in transaction fixtures in specs for Rails 4, a workaround for Rails versions less than 5 is to use run_callbacks. Issue has been fixed in Rails 5. So we add a version check on spec. See https://stackoverflow.com/a/30901628/15768801 for more details.
Changes