Preliminary Findings on Test Passes Alone
The test passes when run by itself. The test fails in the full suite. The test has not changed. Something else changed.
PRELIMINARY FINDINGS Subject: Test passing in isolation, failing in suite. Classification: Environment-dependent behavior.
The Evidence
Individual run: PASS. Full suite run: FAIL. Test code: unchanged. Test output when failing: an assertion error indicating a value is null when a non-null value is expected.
The Initial Hypotheses
The test expects a non-null value. In isolation, the value is non-null. In the suite, the value is null. Something between the other tests and this test is producing null.
Hypothesis A: Another test is cleaning up a shared resource that this test expects to exist. Hypothesis B: Another test is setting a global state that this test is reading, and when not set (in isolation), the code takes a different path that produces non-null. Hypothesis C: The test order in the suite places this test after a test that corrupts the relevant state. Hypothesis D: The test is not properly isolated and depends on side effects from its own previous runs.
The Investigation
The failing test's position in the suite: 47 of 83. The tests before it were examined for shared resource modification.
Test 31: Clears the user session. The failing test, test 47, reads the user session. In isolation, the session has a default value. In the suite, after test 31, the session is cleared.
The Finding
Hypothesis A was correct. Test 31 clears the session. Test 47 reads it. In isolation, the session has a test default. After test 31, there is no session.
The fix: test 47 must set up its own session state rather than depending on a default.
The test was updated. The suite passes.