#6 - Ensure only valid Customers can be stored

In this issue we will implement the very first test case to back up our implementation of storing customers.

• create Junit 5 Test
• interact with the DataManager in a Spring Integration Test
• use assertJ to assert the customer was correctly saved
• Use SystemAuthenticator to authenticate in an integration test
• Use Bean validation explicitly in the integration test to check for proper bean validation annotations are present