Use sub tests for HandlerTests
Use sub tests for HandlerTests

For better output.

PiperOrigin-RevId: 295999390
Change-Id: I0054c31dd1084b5b9ea5ab9f229aee3eb17eec90

GoogleCloudPlatform/healthcare-federated-access-services,GoogleCloudPlatform/healthcare-federated-access-services,GoogleCloudPlatform/healthcare-federated-access-services,GoogleCloudPlatform/healthcare-federated-access-services