How to put a customized message in K6 Check

I am running a K6 tests with request.batch where number of requests can change for each test.

req = [req0, req1, req2, ...];
let res = http.batch(req);

then, I am trying to run a "check" for each request, and I use a while loop to do so.

while (i < req.length) {
    check(
      res[i],
      {" ${i} - status 200": (r) => r.status === 200 }
    );
    i++;
}

however K6 accumulate all "check" tests results in a single test, as test message doesn't parse the variable I pass. the output prints this message at the end of the test:

done [===============] 10s / 10s
✓  ${i} - status 200

I have tried to use different ways add the parameters, but no use:

{ i + " - status 200": (r) => r.status === 200 }
{' ${i} - status 200': (r) => r.status === 200 }
{` ${i} - status 200`: (r) => r.status === 200 }
{" %d - status 200", i : (r) => r.status === 200 }

I would like to know if there is any why to pass a customized message here.

Solution

You can use the bracket notation for assigning the property name.

See the example below and the following link: How to create an object property from a variable value in JavaScript?

import http from "k6/http";
import { check } from "k6";

export default function() {
    let response = http.get("https://test.loadimpact.com");
    let test = "x";
    check(response, {
        [test + " - status 200"]: (r) => r.status === 200
    });
};

This results in the following output:

done [==========================================================] 1 / 1i

✓ x - status 200 

checks.....................: 100.00% ✓ 1   ✗ 0
data_received..............: 6.8 kB  15 kB/s
data_sent..................: 527 B   1.2 kB/s
http_req_blocked...........: avg=362.37ms min=362.37ms med=362.37ms max=362.37ms p(90)=362.37ms p(95)=362.37ms
http_req_connecting........: avg=138.16ms min=138.16ms med=138.16ms max=138.16ms p(90)=138.16ms p(95)=138.16ms
http_req_duration..........: avg=91.62ms  min=91.62ms  med=91.62ms  max=91.62ms  p(90)=91.62ms  p(95)=91.62ms
http_req_receiving.........: avg=0s       min=0s       med=0s       max=0s       p(90)=0s       p(95)=0s
http_req_sending...........: avg=992.2µs  min=992.2µs  med=992.2µs  max=992.2µs  p(90)=992.2µs  p(95)=992.2µs
http_req_tls_handshaking...: avg=214.19ms min=214.19ms med=214.19ms max=214.19ms p(90)=214.19ms p(95)=214.19ms
http_req_waiting...........: avg=90.63ms  min=90.63ms  med=90.63ms  max=90.63ms  p(90)=90.63ms  p(95)=90.63ms
http_reqs..................: 1       2.207509/s
iteration_duration.........: avg=453.99ms min=453.99ms med=453.99ms max=453.99ms p(90)=453.99ms p(95)=453.99ms
iterations.................: 1       2.207509/s
vus........................: 1       min=1 max=1
vus_max....................: 1       min=1 max=1