Fix Flaky Test

Quick Start

You’ll typically receive a Tuist test case URL or identifier. Follow these steps to investigate and fix it:

1. Run tuist test case show <id-or-identifier> --json to get reliability metrics for the test.
2. Run tuist test case run list Module/Suite/TestCase --flaky --json to see flaky run patterns.
3. Run tuist test case run show <run-id> --json on failing flaky runs to get failure messages and file paths.
4. Read the test source at the reported path and line, identify the flaky pattern, and fix it.
5. Verify by running the test multiple times to confirm it passes consistently.

Investigation

1. Get test case metrics

You can pass either the UUID or the Module/Suite/TestCase identifier:

tuist test case show <id> --json
tuist test case show Module/Suite/TestCase --json

Key fields:

• reliability_rate — percentage of successful runs (higher is better)
• flakiness_rate — percentage of runs marked flaky in the last 30 days
• total_runs / failed_runs — volume context
• last_status — current state

2. View flaky run history

tuist test case run list Module/Suite/TestCase --flaky --json

The identifier uses the format ModuleName/SuiteName/TestCaseName or ModuleName/TestCaseName when there is no suite. This returns only runs that were detected as flaky.

3. View full run history

tuist test case run list Module/Suite/TestCase --json --page-size 20

Look for patterns:

• Does it fail on specific branches?
• Does it fail only on CI (is_ci: true) or also locally?
• Are failures clustered around specific commits?

4. Get failure details

tuist test case run show <run-id> --json

Key fields:

• failures[].message — the assertion or error message
• failures[].path — source file path
• failures[].line_number — exact line of failure
• failures[].issue_type — type of issue (assertion_failure, etc.)
• repetitions — if present, shows retry behavior (pass/fail sequence)
• test_run_id — the broader test run this execution belongs to

Code Analysis

1. Open the file at failures[0].path and go to failures[0].line_number.
2. Read the full test function and its setup/teardown.
3. Identify which of the common flaky patterns below applies.
4. Check if the test shares state with other tests in the same suite.

Common Flaky Patterns

Timing and async issues

• Missing waits: Test checks a result before an async operation completes. Fix: use await, expectations with timeouts, or polling.
• Race conditions: Multiple concurrent operations access shared state. Fix: synchronize access or use serial queues.
• Hardcoded timeouts: sleep(1) or fixed delays that are too short on CI. Fix: use condition-based waits instead of fixed delays.

Shared state

• Test pollution: One test modifies global/static state that another test depends on. Fix: reset state in setUp/tearDown or use unique instances per test.
• Singleton contamination: Shared singletons carry state between tests. Fix: inject dependencies or reset singletons.
• File system leftovers: Tests leave files that affect subsequent runs. Fix: use temporary directories and clean up.

Environment dependencies

• Network calls: Tests hit real services that may be slow or unavailable. Fix: mock network calls.
• Date/time sensitivity: Tests depend on current time or timezone. Fix: inject a clock or freeze time.
• File system paths: Hardcoded paths that differ between environments. Fix: use relative paths or temp directories.

Order dependence

• Implicit ordering: Test passes only when run after another test that sets up required state. Fix: make each test self-contained.
• Parallel execution conflicts: Tests that work in isolation but fail when run concurrently. Fix: use unique resources per test.

Fix Implementation

After identifying the pattern:

1. Apply the smallest fix that addresses the root cause.
2. Do not refactor unrelated code.
3. If the fix requires a test utility (like a mock or helper), check if one already exists before creating a new one.

Verification

Run the specific test repeatedly until failure using xcodebuild‘s built-in repetition support:

xcodebuild test -workspace <workspace> -scheme <scheme> -only-testing <module>/<suite>/<test> -test-iterations <count> -run-tests-until-failure

This runs the test up to <count> times and stops at the first failure. Choose the iteration count based on how long the test takes — for fast unit tests use 50–100, for slower integration or acceptance tests use 2–5.

Done Checklist

• Identified the root cause of flakiness
• Applied a targeted fix
• Verified the test passes consistently (multiple runs)
• Did not introduce new test dependencies or shared state
• Committed the fix with a descriptive message