k6 - storing data between setup and default functions

Question

I want to store an id in a setup section, what I got when I upload a file for an endpoint, and after that, I need to get back the uploaded element in the default section multiple times. I tried to use a helper function with a setter and getter but it gave back undefined in the default function. Is there any easy way to store a number between the setup function and the default?

Answer 1

Yes, that is possible and it is documented and explained in Test Life Cycle – Setup and Teardown Stages.

The setup function can return an object, which is then passed to each VU's default function as the first parameter:

import http from 'k6/http';

export function setup() {
  const res = http.get('https://httpbin.test.k6.io/get');
  return { data: res.json() };
}
export function teardown(data) {
  console.log(JSON.stringify(data));
}

export default function (data) {
  console.log(JSON.stringify(data));
}

There are some restrictions regarding the data types you can pass between setup and default or teardown, but you mentioned it being a number which should be no problem. Basically anything is supported, as long as it can be serialized to and from JSON.

For your use-case it would probably look like this:

import http from 'k6/http';

const file = open('./path/to/file', 'b');

export function setup() {
  const uploadData = {
    fileUploadFieldName: http.file(file, 'yourfilename'),
  };

  const res = http.post('https://example.com/upload', uploadData);
  return { documentId: res.json('document.id') };
}

export default function (data) {
  const res = http.get(http.url`https://example.com/documents/${data.documentId}`);
  // ...
}