A flaky Cypress test passes sometimes and fails other times without a relevant code change. Find the cause by reproducing the failure under controlled conditions, then look for nondeterministic setup, brittle selectors, guessed timing, or decisions based on a changing page. Fix the underlying dependency and verify the test alone, in its suite, and under varied load; increasing retries by itself does not make a test reliable.
What makes a Cypress test flaky?
A test is flaky when the same code produces inconsistent results across runs. Often, the test assumes a particular state, timing, or resource condition that is not guaranteed. Cypress lists animations, API calls, server or database availability, resource availability, and network issues among possible sources of race conditions. Treat these as hypotheses to investigate, not automatic explanations for every failure. Cypress’s test-retry guidance describes these failure sources.
Two different Cypress behaviors are easy to confuse:
- Query retry-ability: Cypress re-runs linked queries and assertions until they pass or time out. Commands that are not queries execute once. This lets a test wait for the condition it needs instead of sleeping for an estimated duration. See Cypress’s retry-ability documentation.
- Test retries: When configured, Cypress reruns a whole failed test for a specified number of additional attempts. Retries are disabled by default. A test that fails and then passes on a retry has exposed nondeterminism; that later pass does not prove the cause is fixed. See Cypress’s test-retry guidance.
How to investigate an intermittent failure
Preserve the conditions of the failure
Before changing the test, keep the failing assertion and command log, and record the browser, test data, Cypress version, operating environment, and whether the failure occurred in cypress open or cypress run. These details help distinguish a reproducible test defect from a difference in runtime conditions.
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Run the test at different scopes
- Run the suspect test by itself. If it fails alone, focus first on its own setup, synchronization, selectors, and dependencies.
- Run it in its spec, then in the normal suite. If it fails only alongside other tests, investigate shared state, ordering, and cleanup.
- Repeat the test to try to expose intermittent behavior. Cypress recommends excessive repetition; its documentation gives 100 executions as an example, not a universal or statistically meaningful threshold.
- Throttle network and CPU conditions to simulate different loads. A failure that appears only under slower conditions can point to a timing or resource assumption worth testing.
For each failure, note the exact command and assertion that failed, whether the page reached the expected state, and whether a preceding test or request changed the conditions. Change one suspected cause at a time so that the next run provides useful evidence.
Use the symptom to choose what to inspect
- An element times out: Check whether the application reached the required state, whether the selector still matches the intended element, and whether the test depends on an asynchronous action that has not completed.
- The test fails only after another test: Check for browser or server-side state left behind, ordering assumptions, and cleanup that runs only after the test.
- The test fails under CI-like load: Reproduce with network or CPU throttling and look for guessed delays, slow dependencies, and resource assumptions.
- The failure appears inconsistent without an obvious pattern: Preserve each run’s context and examine asynchronous requests, animation, and backend availability rather than assuming a longer timeout is the answer.
These are starting points for diagnosis, not proof of a particular cause.
Code smells that make Cypress tests flaky
1. A test relies on another test’s leftovers
Smell: A test assumes another test has logged in, created a record, or navigated to a particular page. It passes in the full suite but fails when run alone or reordered.
Fix: Make each test establish its own starting conditions and data. Cypress enables end-to-end test isolation by default, but browser isolation does not necessarily reset server-side records or other backend state. Arrange setup or reset deliberately for data that can be changed by one test and observed by another. Cypress calls test independence a best practice in its test-isolation documentation.
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Programmatic login can avoid repeating UI login steps in every test, but keep a separate test of the actual login flow so that setup shortcuts do not leave that user-facing behavior untested. Cypress discusses isolated specs, programmatic login, and controlling application state in its best-practices guidance.
2. Selectors depend on styling or implementation details
Smell: A test locates a control through a long CSS path or a class used for presentation. A markup or styling change can then break the test even when the user-visible behavior is unchanged.
Fix: Give important test targets purposeful, specific data-* attributes, such as data-cy, and select by that attribute. For example, use cy.get('[data-cy="save-profile"]') rather than a selector coupled to layout classes. Choose a project-wide convention and avoid ambiguous attributes that match multiple controls. Cypress recommends data-* attributes because they separate selectors from CSS and JavaScript changes in its best-practices guidance.
3. A fixed wait guesses when the page will be ready
Smell: The test uses a delay such as cy.wait(5000) to guess when rendering or a request will finish. If the app is slower, the guess is too short; if it is faster, the test wastes time.
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Fix: Assert the state the test needs. Cypress retries linked queries and assertions until they pass or time out, so a test can express a condition rather than a duration:
cy.get('[data-cy="save-status"]').should('have.text', 'Saved')For a known network request, use an explicit request boundary and then assert the UI result. For example:
cy.intercept('GET', '/api/profile').as('getProfile')
cy.visit('/profile')
cy.wait('@getProfile')
cy.get('[data-cy="profile-name"]').should('be.visible')The aliased wait synchronizes on a specific intercepted request; the following assertion checks that the page reached the state the test cares about. A bare time-based wait is not the same thing as waiting for a known request. See Cypress’s retry-ability documentation and its guidance on test retries and timeouts.
4. The test branches on a DOM that is still changing
Smell: The test checks whether a transient element exists and takes a different path while the client application may still be rendering or updating. The observed DOM can differ across runs.
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Fix: Make the application behavior deterministic, or base the decision on a stable source of truth, such as explicit test data, server state, a cookie, or local storage. For example, control an experiment with a URL parameter rather than guessing whether a changing page has rendered a particular variant. Conditional DOM checks are safe only when the page is known to have settled. Cypress explains the limits of conditional testing.
5. Required cleanup happens only after a test
Smell: A database or application reset is only in after or afterEach. If the runner is refreshed mid-test, that cleanup may not run, leaving stale data for later tests.
Fix: Put required setup or reset before each test so that the test establishes its own preconditions. First check whether Cypress’s automatic browser isolation already handles the state in question; reset server-side data separately when needed. See Cypress’s best-practices guidance.
6. More test retries are treated as the repair
Smell: A team increases the retry count, sees a later pass, and stops investigating the original failure.
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Fix: Use retry results to make intermittent failures visible and to guide triage, not to certify a test as deterministic. When retries are configured, the count is the number of additional attempts, and beforeEach and afterEach run again for each attempt. Keep the failure history and find the test’s underlying dependency before treating the work as complete. Cypress’s retry behavior and configuration are covered in its test-retry documentation.
How to verify a fix
- Run the changed test alone, then in its spec and normal suite.
- Repeat it under different network and CPU conditions, including throttling. Cypress recommends repeating tests and varying load; the 100-run example in its guidance is illustrative, not a universal pass threshold. See Cypress’s advice on reproducing flaky behavior.
- Run relevant neighboring tests to check that the change did not introduce shared-state leakage or ordering dependence.
- Confirm the user-visible condition with an assertion. Do not infer that a command completed merely because a guessed duration elapsed.
- Record the Cypress version, browser, environment, and whether the test ran in
cypress openorcypress run, so a recurrence can be compared against the original conditions.
A useful fix makes setup deterministic, selectors resilient to presentation changes, synchronization specific to the required condition, and recurring failures diagnosable. If a retry passes, retain that evidence as a signal to keep investigating rather than as the verification result.
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When Cypress’s experimental flake detection is relevant
Cypress’s current documentation also describes experimental retry strategies for flake detection, including approaches that can preserve a failing result after a later passing retry or require a threshold of passing attempts. These options are experimental and may change; verify their configuration against the Cypress version your project uses before adopting them. They can help teams surface and manage flaky outcomes, but do not replace fixing nondeterministic test setup or synchronization. See Cypress’s test-retry documentation.
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