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If a test suite starts failing after its runner stops executing tests in the same order, the order change is a clue—not proof of the cause. A test that passes in one order and fails in another fits the definition of an order-dependent flaky test. The title does not identify the runner, version, configuration change, failure messages, or repository, so the first step is to establish what changed and reproduce the failures under controlled orders.
Why did tests fail when the runner changed their order?
One possibility is that a failing test depends on state left behind by an earlier test. That state might be in the process, a database, the filesystem, an environment variable, or another resource. When execution order changes, the test may run before the state it expected has been created—or after another test has changed it.
Order alone does not establish that explanation. A runner update, a command-line option, a plugin, changed test discovery, or parallel execution could also coincide with the failures. The available incident details do not identify which of these occurred, or independently confirm that 37 tests failed.
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How to determine what changed
- Record the execution environment. Note the runner and version, exact command, plugins, CI configuration, and any recent update or option change. The incident description does not provide these details.
- Capture both sequences. Use the runner’s collection or verbose output, where available, to compare the old order with the new one. Check for randomization, parallel execution, failed-tests-first behavior, or changes to test discovery.
- Save each failure. Keep the test name and complete failure output, along with the command and relevant environment details. This gives you something concrete to compare across runs.
- Repeat the changed run consistently. Preserve the same environment and inputs. If the runner supports a random seed, record and reuse it so you can check whether the same order produces the same failures. The reproduction command depends on the runner; the incident details do not establish one.
How to find a test-order dependency
- Run a failing test by itself. If it passes alone but fails in the suite, that points toward an interaction worth investigating; it does not by itself identify the cause.
- Add likely predecessors. Run the failing test with tests that came before it in the failing sequence. If the failure follows a particular predecessor, inspect what that test changes and whether it restores the affected state.
- Check shared resources and cleanup. Investigate process-level state, databases, files and temporary directories, environment variables, clocks, network services, and teardown behavior as hypotheses. These are common places to look, not established facts about this incident.
- Compare multiple sequences. Reproduce the failure with the changed order, then test other orders where practical. A failure that tracks a particular test interaction is more informative than a failure that merely coincides with a general order change.
The 2019 paper iFixFlakies: A Framework for Automatically Fixing Order-Dependent Flaky Tests defines an order-dependent test in terms of passing in at least one order and failing in another. It is useful research context, but it does not establish the cause of this incident or show that an automated fix applies to its code.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to fix the underlying problem and verify it
Where a dependency is confirmed, make each test establish the state it needs and clean up what it changes. Prefer explicit setup and teardown over relying on another test to prepare or reset a resource. Then verify the formerly failing tests both alone and in the full suite under more than one order.
Pinning the old order may be a temporary containment measure if a specific CI constraint requires it, but it does not remove a hidden dependency. Treat it as containment, not a durable repair, and do not claim the issue is fixed until the relevant runs have actually passed. The pytest documentation index links to guidance on flaky-test causes and testing strategies; consult documentation for the actual runner and version before applying framework-specific instructions.
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