Document hard-coded implicit delay in Node.js

[jlissner]

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It says that it waits ~100-400ms by default, but that is not always the case. From the source code:

function getRealisticResponseTime(): number {
  if (isNodeProcess()) {
    return NODE_SERVER_RESPONSE_TIME
  }

  return Math.floor(
    Math.random() * (MAX_SERVER_RESPONSE_TIME - MIN_SERVER_RESPONSE_TIME) +
      MIN_SERVER_RESPONSE_TIME,
  )
}

So if it's determined to be a node process, it always returns 5. I'm using msw for testing a react app, so while it's running on a node process, that is not the desired behavior. Additionally, the docs make no mention of this "feature", which I had to dig into the source code to understand why thing's weren't being delayed as expected.

[kettanaito]

Hi, @jlissner. Thanks for bringing this up.

Yes, that's indeed an implicit feature designed to provide a better testing experience since in the light of how the realistic server response time is used with the delay() function.

MSW intends that use case to enable server-like response times when developing, but when testing you want your network to be fast. That's why we preemptively hard-code the realistic response time to a fixed value when run in Node.js. Your tests should be reliable and reproducible, which means a reliable and reproducible network that MSW aims to provide, including the fixed response timing when using the delay() function without any arguments.

You can opt-out from this by providing an explicit delay duration to the delay() function. In that case, MSW will respect it as-is.

I do believe this behavior makes sense, we just need to document it better on the website.

[jlissner]

Thanks for the answer! I think a nice-to-have would be to explicitly state if you want browser or server default/real delays. That being said, just having it documents would be great though :).