Handling Flaky Tests in Cypress: Best Practices and Strategies
Tags: webdev, javascript, testing, cypress
Published: 2024-07-14 11:18:14

## Introduction
Flaky tests are a common challenge in automated testing. They are tests that sometimes pass and sometimes fail for reasons unrelated to code changes, leading to inconsistent and unreliable test results. In this post, we’ll explore the causes of flaky tests in Cypress and discuss best practices and strategies to handle them effectively.

## What Are Flaky Tests?
Flaky tests are tests that exhibit non-deterministic behavior, meaning they don't always produce the same result when run under the same conditions. This inconsistency can undermine the reliability of your test suite and erode confidence in your automated tests.

## Common Causes of Flaky Tests

1. **Timing Issues:** Tests that depend on asynchronous operations or dynamic content loading can fail if the expected conditions are not met within the given time.
2. **Environment Dependence:** Tests that are influenced by external factors like network speed, server response time, or environment configuration can be flaky.
3. **Resource Contention:** Tests that rely on shared resources or perform actions that affect the state of the application can cause race conditions.
4. **Dependencies on External Services:** Tests that depend on third-party APIs or services can fail due to external service downtime or rate limiting.
5. **Improper Test Isolation:** Tests that do not properly reset or isolate the application state can fail due to leftover data or side effects from previous tests.

## Best Practices for Handling Flaky Tests in Cypress

- **Use `cy.intercept()` for Network Requests:** Stub network requests to control the responses and reduce dependency on external services.

```js
cy.intercept('GET', '/api/data', { fixture: 'data.json' }).as('getData');
cy.visit('/');
cy.wait('@getData');
```
- **Leverage `cy.wait()` Wisely:** Use `cy.wait()` to wait for specific conditions or events instead of arbitrary time periods.

```js
cy.get('.spinner').should('not.exist'); // Ensure spinner is gone
cy.get('.data-list').should('be.visible'); // Ensure data list is visible
```
- **Implement Custom Commands:** Create custom commands to encapsulate common actions and ensure they are performed consistently.

```js
Cypress.Commands.add('login', (username, password) => {
    cy.get('input[name="username"]').type(username);
    cy.get('input[name="password"]').type(password);
    cy.get('button[type="submit"]').click();
    cy.url().should('include', '/dashboard');
});
```
- **Use `cy.retry()` Plugin:** Install the Cypress retry plugin to automatically retry failed assertions.

```js
// Install the plugin first: npm install -D cypress-plugin-retries
require('cypress-plugin-retries');

// Enable retries in your test
Cypress.env('RETRIES', 2);

// Example test with retries
it('should display data after retry', () => {
    cy.visit('/data-page');
    cy.get('.data-item').should('have.length', 10); // Retry if fails
});
```
- **Isolate Tests:** Ensure each test runs in isolation by properly resetting the application state before and after each test.

```js
beforeEach(() => {
    cy.exec('npm run reset-db'); // Reset the database
    cy.visit('/');
});
```
- **Optimize Selectors:** Use robust and stable selectors to target elements, reducing the likelihood of selector-related flakiness.

```js
// Use data attributes for selectors
cy.get('[data-cy="submit-button"]').click();
```

## Debugging Flaky Tests

1. **Run Tests Locally:** Run the flaky test locally using `cypress open` to observe its behavior and identify potential issues.
2. **Use Debugging Tools:** Utilize Cypress’s built-in debugging tools like `cy.debug()` and browser DevTools to inspect the application state.
3. **Analyze Logs and Screenshots:** Review Cypress logs, screenshots, and videos to pinpoint the cause of flakiness.

## Example: Handling a Flaky Test in Cypress

```js
describe('Flaky Test Example', () => {
    beforeEach(() => {
        cy.visit('/');
    });

    it('should load data reliably', () => {
        // Use intercept to stub network request
        cy.intercept('GET', '/api/data', { fixture: 'data.json' }).as('getData');
        cy.get('button[data-cy="load-data"]').click();
        cy.wait('@getData');

        // Use robust selector and assertion
        cy.get('[data-cy="data-list"]').should('have.length', 5);
    });

    it('should handle spinner correctly', () => {
        // Ensure spinner is not visible before asserting data
        cy.get('.spinner').should('not.exist');
        cy.get('[data-cy="data-list"]').should('be.visible');
    });
});

```

## Conclusion
Handling flaky tests is crucial for maintaining a reliable and robust test suite. By understanding the common causes of flakiness and implementing best practices, you can significantly reduce the occurrence of flaky tests in your Cypress projects. Remember to leverage Cypress’s powerful features and tools to ensure your tests are deterministic, isolated, and stable.

Happy testing!