enter
assertThat(pVariablesInReturn).isWaitingAt("actvityIdWithAcyncBefore");
execute(job());
between the start and the end of the process instance in your test.
You can read more about the details here: Transactions in Processes | docs.camunda.org
The shortcut in camunda-bpm-assert is documented in the github repository: camunda-bpm-assert/User_Guide_BPMN.md at master · camunda/camunda-bpm-assert · GitHub.
Hope this helps, Ingo