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Decision note: a fresh session for every test

ClientSimTestBase ends its ClientSim session after every test, and the next test starts its own. A session ends completely: End leaves nothing of ClientSim running. The one thing that carries over is saved data, and the kit never deletes it unless a test asks.

Why tests don't share a session​

A test that starts from a fresh session can't depend on what an earlier test did, so each test passes or fails on its own, in any order. NUnit doesn't promise an order between tests, so a test that only passes after another one fails at random. In xUnit Test Patterns terms, this is a fresh fixture.

Ending a session completely also lets one test use more than one session. A test can end a session and start another in the same scene to check that data survives a rejoin, without relying on the order of tests.

Why saved data carries over​

Carrying over is what saved data is for, and ClientSim keeps it in files, not in the session. The kit never deletes those files on its own. In your world's own scene, they're your ClientSim data, and some worlds want them to carry over between tests. ClientSimSession.DeleteSavedData is there for a test that needs none.

Alternatives considered​

  • One session for a whole test class — faster, since ClientSim starts once, but every test then shares whatever the earlier ones changed: players, owners, saved data and every object in the scene. That's xUnit Test Patterns shared fixture, and its known cost is tests that depend on each other. It stays possible for tests that only read, by starting the session in a [UnitySetUp] when it isn't running yet and ending it in [OneTimeTearDown].
  • Deleting saved data after every test — every test would start clean, but tests run in the world's own scene would delete the developer's ClientSim data, and a test of data carrying over couldn't be written.

Scenes follow the same rule​

Every test in a Play Mode run shares the Unity Test Framework test scene by default. A TestScene with the default PerTest lifetime gives each test a fresh copy of its own scene, and PerFixture is the shared option, for tests that don't change it.