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⚠️ This is the archived documentation for k6 v0.47. Go to the latest version.

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.

ParameterTypeDescription
valanyValue to test.
setsobjectTests (checks) to run on the value.
tags (optional)objectExtra tags to attach to metrics emitted.

Returns

TypeDescription
booleantrue 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');
}
}