A unit test should be deterministic.

A deterministic unit test is one that produces the same results every time it is run under the same conditions. This characteristic is crucial for unit tests because it ensures that the tests are reliable and that their results are repeatable. Deterministic tests help in identifying when a change in the codebase has introduced a defect, as any variation in the test outcome can be attributed to the change rather than an unpredictable test behavior12.

References = The ISTQB Advanced Level Agile Technical Tester syllabus and study resources emphasize the importance of deterministic behavior in unit tests as part of ensuring test reliability and effectiveness34.