Persistence testing is done so basic, writing your first unit test will make you cry.
Lets write a test, that says we have corrected Hibernate handling of UUID Primary Keys
Each piece of this test is highlighted in red

I want a test that doesn't need to test transaction management, and will obtain the database connections from an existing wildfly standalone file, using EntityAssist to simply query execution 
@Test
public void testUUIDHibernatePrimaryKeyFromWildfly()
{
	WildflyConnectionInfoBuilder.setStandaloneFileName("standalone-full-ha.xml");
	BTMAutomatedTransactionHandler.setActive(true);
	TestEntity api = new TestEntity()
			.setOID(UUID.randomUUID())
			.persist();
	Optional stored = new TestEntity().builder().find(api.getOid()).get();
	assertEquals(stored.get().getOid(),api.getOid());
}

You can swap out DatabaseModule's using Guiced EE's module loading mechanism, or even just change the referenced persistence unit name in the module to point to a different location if you want more than one persistence units available for unit testing 
Set modules = GuiceContext.instance().loadIGuiceModules();
modules.removeIf(a -> a.getClass().equals(MyDataBaseModule.class));
modules.add(new MyDatabaseModuleTests());

Dynamically setting your module persistence unit name can be done as shown below 
public MyDatabaseModule()
{
  if (StaticConfiguration.getRunningEnvironment()
	   .equals(RunningEnvironment.UnitTest))
  {
    setPersistenceUnitName(getPersistenceUnitName() + "_UT");
  }
}
@Override
public String getPersistenceUnitName()
{
	return PersistenceUnitName;
}


Creating keys for your DatabaseModules can be very handy, especially for getting a hold of instances directly without using injection 
public static final Key MODEL_DATASOURCE_KEY = Key.get(DataSource.class, MyDatabaseAnnotation.class);
public static final Key MODEL_ENTITYMANAGER_KEY = Key.get(EntityManager.class, MyDatabaseAnnotation.class);

I am then able to get a hold of these instances directly in my test class : 
EntityManager em = GuiceContext.get(MyDatabaseBModule.MODEL_ENTITYMANAGER_KEY);
assertTrue(em.isOpen());