A Sub Test Execution has exactly the same functionalities as the Test Execution issue type. The difference between them is that the Sub Test Execution is a sub-task and can be created in a requirement's context.
Creating a Test Execution as a sub-task of the requirement issue will provide the user the ability to track executions in the Agile's board.
Create Sub Test Executions
In order to create a new Sub Test Execution, the user must click the Create new Test Execution button in the Test Coverage section in the Requirement Issue View:
Remember to Associate Tests and Test Sets with the Sub Test Execution.