Why is cypress slow?

Answered by Randy McIntyre

Cypress can be slow for a few reasons, but one of the main factors is the need to run a proxy on 3rd party browsers. This proxy is required in order to record the requests being sent and received. While this is necessary for Cypress to function properly and provide its powerful testing capabilities, it can significantly slow down load times.

When Cypress runs tests, it intercepts and modifies network requests made by the application under test. This allows it to control and manipulate the application’s behavior, which is crucial for testing purposes. However, intercepting requests requires the use of a proxy server that sits between the browser and the application. This proxy server captures the network traffic and allows Cypress to inspect and modify it.

The process of intercepting and modifying requests adds an extra layer of complexity and can introduce some latency. Each request made by the application needs to be intercepted, processed, and then forwarded to its intended destination. This additional overhead can slow down the overall execution of tests.

Moreover, running a proxy on 3rd party browsers can be particularly challenging because Cypress has to support multiple browsers and their different networking behaviors. Each browser may have its own set of quirks and limitations, which Cypress needs to handle appropriately. This can require additional time and effort to ensure compatibility and reliable testing across different browsers.

Additionally, Cypress aims to provide a reliable and deterministic testing experience. It achieves this by waiting for certain conditions to be met before proceeding with the test execution. For example, Cypress waits for elements to become visible or for network requests to complete before moving on to the next step. While this ensures consistent test results, it can also contribute to longer execution times.

Furthermore, Cypress’s architecture is built around a single-threaded event loop. This means that all test commands and assertions run sequentially, one after another. While this simplifies the test development process and ensures consistent test execution, it can also impact performance, especially when dealing with long-running tests or extensive test suites.

To mitigate some of the performance issues, Cypress provides various configuration options and best practices. For example, disabling certain network requests or using stubs instead of making actual requests can help reduce the overhead introduced by the proxy. Additionally, optimizing test code and avoiding unnecessary waiting can improve execution times.

Cypress can be slow due to the need to run a proxy on 3rd party browsers, which introduces additional complexity and latency. The interception and modification of network requests, support for multiple browsers, deterministic testing approach, and single-threaded event loop all contribute to the potential slowdown. However, with proper configuration and optimization, it is possible to mitigate some of these performance issues and improve the overall testing experience with Cypress.