Test Isolation¶

Tests that share state create order-dependent failures, making the test suite non-deterministic and failures harder to reproduce; isolation ensures each test starts from a known state and cannot corrupt the environment for other tests.

Tension Addressed¶

Isolation vs. Integration

Recognizable As¶

setUp/tearDown methods; test database transactions that rollback; fresh object instantiation per test; avoiding static mutable state; test parallelization without failures

Canonical Sources¶

Meszaros, "xUnit Test Patterns" (2007); Beck, "Test-Driven Development" (2002)

Transfers To¶

Scientific method (controlled experiments); database transactions (ACID isolation); process isolation in operating systems; reproducibility in research

Isolation is a prerequisite for reliable test suites. When tests share state, a passing test suite can hide failures that only manifest when tests run in a different order - the resulting non-determinism undermines trust in the entire suite.