What is the importance of End to end testing for performance and scalability?

End to end testing is often associated with validating user flows, but it can also reveal how applications behave under realistic performance and scalability scenarios. Unlike synthetic load testing, end to end tests simulate the complete chain of services, databases, and third-party integrations that a user action triggers.

For example, a simple checkout flow may pass functionally with 10 users, but under 1,000 concurrent sessions it could expose hidden bottlenecks in database queries, caching layers, or API response times. Running end to end testing with performance parameters helps teams detect issues that unit or isolated load tests can’t uncover.

Teams adopting this approach often combine functional assertions with performance metrics like latency, throughput, and error rates. Keploy’s ability to generate tests and mocks from live traffic can complement this by ensuring that scalability tests reflect real usage patterns rather than synthetic assumptions. This leads to more reliable results and fewer surprises in production.