check( val, sets, [tags] )

Run checks on a value. A check is a test condition that can give a truthy or falsy result. The sets parameter contains one or more checks, and the check() function will return false if any of them fail.

Note that checks are not asserts in their traditional sense - a failed assertion will throw an error, while a check will always return with a pass or a failure. Failure conditions can then instead be controlled by thresholds, for more power and flexibility.

Parameter	Type	Description
val	any	Value to test.
sets	object	Tests (checks) to run on the value.
tags (optional)	object	Extra tags to attach to metrics emitted.

Returns

Type	Description
boolean	`true` if all checks have succeeded, `false` otherwise.

Examples

Using check() to verify that an HTTP response code was 200:

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

export default function () {
  const res = http.get('https://httpbin.test.k6.io');
  check(res, {
    'response code was 200': (res) => res.status == 200,
  });
}

Using check() with a custom tag to verify that an HTTP response code was 200 and that body was 1234 bytes. The checkOutput can be used for any condition in your script logic:

import http from 'k6/http';
import { check, fail } from 'k6';

export default function () {
  const res = http.get('https://httpbin.test.k6.io');
  const checkOutput = check(
    res,
    {
      'response code was 200': (res) => res.status == 200,
      'body size was 1234 bytes': (res) => res.body.length == 1234,
    },
    { myTag: "I'm a tag" }
  );

  if (!checkOutput) {
    fail('unexpected response');
  }
}