Broadleaf provides its own internal tests via java jars: Broadleaf Dev Central. Here you can find many examples of tests to use as starting points.
Broadleaf also has a public Github repo that has examples of extensibility API tests. These are true REST tests, but are expensive to run. Mixing these with integration tests and unit tests is advisable: GitHub - BroadleafCommerce/MicroservicesConcepts: Various extension and dev use cases. Proving ground for concepts..