k6

The k6 module provides core test functionality including checks, groups, and test control.

The k6 module is the main module that provides core k6 functionality for load testing scripts.

Functions

check(val, sets, [tags])

Runs checks on a value and emits check metrics.

val · any

The value to test

sets · object

Object with check names as keys and check functions as values

tags · object

Optional tags to attach to the check metrics

result · boolean

Returns true if all checks passed, false otherwise

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

export default function () {
  const res = http.get('https://test.k6.io');
  check(res, {
    'status is 200': (r) => r.status === 200,
    'response time < 500ms': (r) => r.timings.duration < 500,
  });
}

fail([message])

Throws an error and interrupts the VU execution.

message · string

Error message to display

import { fail } from 'k6';

export default function () {
  if (someCondition) {
    fail('Test failed due to condition');
  }
}

group(name, fn)

Runs a function within a named group for better organization and metrics.

name · string

Name of the group

fn · function

Function to execute within the group. Must be synchronous.

result · any

Returns the value returned by the function

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

export default function () {
  group('visit homepage', function () {
    http.get('https://test.k6.io');
  });

  group('API tests', function () {
    http.get('https://test.k6.io/api/v1/users');
  });
}

The group() function does not support async functions. Use synchronous functions only.

randomSeed(seed)

Sets the seed for the random generator used for this VU.

seed · integer

Seed value for the random number generator

import { randomSeed } from 'k6';

export default function () {
  randomSeed(12345);
  // Math.random() will now produce deterministic values
}

sleep(seconds)

Suspends VU execution for the specified duration.

seconds · number

Duration in seconds (can be fractional)

import { sleep } from 'k6';

export default function () {
  // Sleep for 1.5 seconds
  sleep(1.5);
}

Examples

Basic Load Test

import { check, group, sleep } from 'k6';
import http from 'k6/http';

export const options = {
  vus: 10,
  duration: '30s',
};

export default function () {
  group('Homepage', function () {
    const res = http.get('https://test.k6.io');
    check(res, {
      'status is 200': (r) => r.status === 200,
    });
  });

  sleep(1);
}