tissue_robots cannot be re-used in selftests
Tissue robots initialize themselves with their robot_agent when the instance is CREATED. Tissue robots are singletons. Therefore, the agent that is given to a robot is constant for the life of the entire PROCESS running the test, not just the unit test where it was used.
IF a python module uses tissue robots in MORE THAN ONE unit test, the agent from the FIRST test has a PK that will not exist by the time the second test is run (because of the setUp and loadTestData initialization of the database).
Fix the tissue_robots so that any database activity happens in the RUN phase, not the INIT phase. This allows the robot to obtain a different agent for each unit test.