Detox End-to-End Tests on CI: A Performance Budget Approach

The Situation

Say you are a lead engineer responsible for a React Native application, and your team has been tasked with improving the performance of your end-to-end tests on your Continuous Integration (CI) pipeline. The symptom you're seeing is that these tests are consistently taking longer than expected to complete, causing delays in your deployment process and impacting your team's productivity. As a result, you're under pressure to make these tests faster, but the requirement is vague, and you need a way to turn it into a measurable goal that your team can work towards.

Why It Happens

Detox end-to-end tests can be slow due to various factors, including the complexity of the tests themselves, the performance of the CI environment, and the overhead of launching and interacting with the application under test. Without a clear understanding of what "faster" means, it's challenging to prioritize optimizations or measure progress. A performance budget approach can help by setting a specific, measurable ceiling for test execution time, providing a clear target for the team to defend.

The Fix, Step by Step

1. Establish a Baseline: Start by measuring the current execution time of your Detox end-to-end tests on your CI pipeline. This will give you a baseline to compare future optimizations against. Use a tool like detox test --loglevel trace to get detailed logs of test execution times.
2. Set a Performance Budget: Based on your application's requirements and the constraints of your CI environment, set a realistic performance budget for your end-to-end tests. For example, you might decide that your tests should not take more than 10 minutes to complete. This budget will serve as your measurable ceiling.
3. Identify Bottlenecks: Use the detailed logs from step 1 to identify the slowest tests and areas where optimizations can have the most significant impact. Look for tests that are consistently taking the longest to complete and prioritize those for optimization.
4. Optimize Tests: Apply optimizations to the identified bottleneck tests, such as reducing the number of interactions, using faster test data, or improving the test environment. For example, you might use detox.init({ launchArgs: { detoxServer: 'ws://localhost:8099' } }) to enable WebSocket-based communication, which can improve test performance.
5. Monitor and Adjust: Continuously monitor your test execution times and adjust your optimizations as needed to ensure you're meeting your performance budget. Use metrics like test execution time, test failure rate, and CI pipeline throughput to guide your decisions.

What It Costs, and When Not to Do It

Implementing a performance budget approach for Detox end-to-end tests on CI requires an upfront investment of time and resources to establish a baseline, set a performance budget, and identify bottlenecks. However, the long-term benefits of faster test execution times, improved productivity, and reduced deployment delays can outweigh the costs. This approach may not be suitable for very small applications or those with extremely simple end-to-end tests, where the overhead of implementing a performance budget may outweigh the benefits.

At Your Level

• Starting out: Focus on understanding the basics of Detox and how to write effective end-to-end tests. As you gain experience, you can start applying the performance budget approach to optimize your tests.
• Working engineer: Use the performance budget approach to identify and optimize bottleneck tests, and work with your team to establish a measurable ceiling for test execution times.
• Senior or staff: Consider the trade-offs between test complexity, test coverage, and test execution time when setting a performance budget, and work with your team to prioritize optimizations that have the most significant impact.
• Lead or director: Use the performance budget approach to set clear, measurable goals for your team, and allocate resources accordingly to ensure that your end-to-end tests are fast, reliable, and effective.

In the Interview

• Question: How would you approach optimizing the performance of Detox end-to-end tests on a CI pipeline?
• Weak answer: "I would just try to make the tests faster by reducing the number of interactions or using faster test data."
• Strong answer: "I would establish a baseline for test execution times, set a realistic performance budget based on the application's requirements and CI environment constraints, identify bottlenecks, and apply targeted optimizations to meet the budget. I would continuously monitor test execution times and adjust optimizations as needed to ensure we're meeting the performance budget."
• Follow-up: "How would you handle a situation where the performance budget is not being met, despite optimizations?" A strong candidate would discuss the trade-offs between test complexity, test coverage, and test execution time, and explain how they would work with the team to prioritize optimizations and allocate resources to meet the performance budget.

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Amit Chakraborty is a founding engineer and senior architect — React Native, AI/RAG systems and production architecture. Portfolio: www.amitchakraborty.dev · LinkedIn · GitHub. Open to senior and founding engineering roles, remote worldwide.