If I require data from the test harness to populate my database, can I assume the test harness will not request an object from me before I have all the data I require?

No. The test harness can’t know what your data dependencies are. It will generate requests as and whenever it sees fit. If you receive a request for an object and you haven’t yet populated your database with data you need from the test harness, you can manually generate another request for yourself using the session request controls on the right-hand side of the agent test session page when you know you have the data to pass a “responds with data” type test. You will not fail the test if you respond with empty response data. The test harness will continue to look for a response with data, which you will be able to provide when you are ready.