An acceptance test is a test that is performed to validate that requirements are met. While RSpec is a fast way to check that a catalog is compiled the way you expect it to be, it does not actually run the catalog on the system and verify that the expected results can be seen. An acceptance test, in the context of Puppet, is applying your selected manifest to a system and verifying that the system meets the requirements after the catalog is applied, preferably with a method that isn't the Puppet Agent itself.
In this chapter, we're going to build an acceptance test for our Jenkins Profile that ensures that Jenkins is running and that we can reach it on port 8080 so that we can view the web page. This extends beyond the ability of RSpec, as Rspec doesn't actually build a node we can verify on. When we use an acceptance testing harness in Puppet, we also tie it to a hypervisor so that it can manage a node, or System Under Test (SUT).