--- title: "expect() | Grafana k6 documentation" description: "BDD style to construct k6 assertions." --- # expect() `expect` is a wrapper of [check](/docs/k6/latest/javascript-api/k6/check/) to provide BDD style of assertions in k6. It implements the [Chai Expect API](https://www.chaijs.com/api/bdd/): - [not](https://www.chaijs.com/api/bdd/#method_not) - [deep](https://www.chaijs.com/api/bdd/#method_deep) - [nested](https://www.chaijs.com/api/bdd/#method_nested) - [own](https://www.chaijs.com/api/bdd/#method_own) - [ordered](https://www.chaijs.com/api/bdd/#method_ordered) - [any](https://www.chaijs.com/api/bdd/#method_any) - [all](https://www.chaijs.com/api/bdd/#method_all) - [a](https://www.chaijs.com/api/bdd/#method_a) - [include](https://www.chaijs.com/api/bdd/#method_include) - [ok](https://www.chaijs.com/api/bdd/#method_ok) - [true](https://www.chaijs.com/api/bdd/#method_true) - [false](https://www.chaijs.com/api/bdd/#method_false) - [null](https://www.chaijs.com/api/bdd/#method_null) - [undefined](https://www.chaijs.com/api/bdd/#method_undefined) - [NaN](https://www.chaijs.com/api/bdd/#method_nan) - [exist](https://www.chaijs.com/api/bdd/#method_exist) - [empty](https://www.chaijs.com/api/bdd/#method_empty) - [arguments](https://www.chaijs.com/api/bdd/#method_arguments) - [equal](https://www.chaijs.com/api/bdd/#method_equal) - [eql](https://www.chaijs.com/api/bdd/#method_eql) - [above](https://www.chaijs.com/api/bdd/#method_above) - [least](https://www.chaijs.com/api/bdd/#method_least) - [below](https://www.chaijs.com/api/bdd/#method_below) - [most](https://www.chaijs.com/api/bdd/#method_most) - [within](https://www.chaijs.com/api/bdd/#method_within) - [instanceof](https://www.chaijs.com/api/bdd/#method_instanceof) - [property](https://www.chaijs.com/api/bdd/#method_property) - [ownPropertyDescriptor](https://www.chaijs.com/api/bdd/#method_ownpropertydescriptor) - [lengthOf](https://www.chaijs.com/api/bdd/#method_lengthOf) - [match](https://www.chaijs.com/api/bdd/#method_match) - [string](https://www.chaijs.com/api/bdd/#method_string) - [keys](https://www.chaijs.com/api/bdd/#method_keys) - [throw](https://www.chaijs.com/api/bdd/#method_throw) - [respondTo](https://www.chaijs.com/api/bdd/#method_respondto) - [itself](https://www.chaijs.com/api/bdd/#method_itself) - [satisfy](https://www.chaijs.com/api/bdd/#method_satisfy) - [closeTo](https://www.chaijs.com/api/bdd/#method_closeto) - [members](https://www.chaijs.com/api/bdd/#method_members) - [oneOf](https://www.chaijs.com/api/bdd/#method_oneOf) - [change](https://www.chaijs.com/api/bdd/#method_change) - [increase](https://www.chaijs.com/api/bdd/#method_increase) - [decrease](https://www.chaijs.com/api/bdd/#method_decrease) - [by](https://www.chaijs.com/api/bdd/#method_by) - [extensible](https://www.chaijs.com/api/bdd/#method_extensible) - [sealed](https://www.chaijs.com/api/bdd/#method_sealed) - [frozen](https://www.chaijs.com/api/bdd/#method_frozen) - [finite](https://www.chaijs.com/api/bdd/#method_finite) JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```javascript import http from 'k6/http'; import { describe, expect } from 'https://jslib.k6.io/k6chaijs/4.3.4.3/index.js'; export default function () { describe('Basic test', () => { expect({ a: 1 }).to.not.have.property('b'); expect(2).to.equal(2); expect({ a: 1 }).to.deep.equal({ a: 1 }); expect({ a: { b: ['x', 'y'] } }).to.have.nested.property('a.b[1]'); expect({ a: 1 }).to.have.own.property('a'); expect([1, 2]).to.have.ordered.members([1, 2]).but.not.have.ordered.members([2, 1]); expect({ a: 1, b: 2 }).to.not.have.any.keys('c', 'd'); expect({ a: 1, b: 2 }).to.have.all.keys('a', 'b'); expect('foo').to.be.a('string'); expect([1, 2, 3]).to.be.an('array').that.includes(2); expect('foobar').to.include('foo'); expect(1).to.equal(1); expect(true).to.be.true; expect(false).to.be.false; expect(null).to.be.null; expect(undefined).to.be.undefined; expect(NaN).to.be.NaN; expect(1).to.equal(1); expect([]).to.be.empty; expect({}).not.to.be.arguments; expect(1).to.equal(1); expect({ a: 1 }).to.eql({ a: 1 }).but.not.equal({ a: 1 }); expect('foo').to.have.lengthOf(3); expect(2).to.equal(2); expect(1).to.equal(1); expect(2).to.be.at.most(3); expect(2).to.equal(2); expect({ a: 1 }).to.not.be.an.instanceof(Array); expect({ a: 1 }).to.have.property('a'); expect([1, 2, 3]).to.have.lengthOf(3); expect('foobar').to.match(/^foo/); expect('foobar').to.have.string('bar'); expect({ a: 1, b: 2 }).to.have.all.keys('a', 'b'); const badFn = function () { throw new TypeError('Illegal salmon!'); }; expect(badFn).to.throw(); expect(1).to.satisfy(function (num) { return num > 0; }); expect(1.5).to.equal(1.5); expect([1, 2, 3]).to.have.members([2, 1, 3]); expect('Today is sunny').to.contain.oneOf(['sunny', 'cloudy']); expect({ a: 1 }).to.be.extensible; expect(1).to.be.finite; }); } ``` When you run this test with `k6 run script.js`, the output at the end of the test shows: Bash ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```bash default ✓ [======================================] 1 VUs 00m00.0s/10m0s 1/1 iters, 1 per VU █ Basic test ✓ expected ${this} to not have property 'b' ✓ expected ${this} to equal 2 ✓ expected ${this} to deeply equal { a: 1 } ✓ expected ${this} to have nested property 'a.b[1]' ✓ expected ${this} to have own property 'a' ✓ expected ${this} to be an array ✓ expected ${this} to have the same ordered members as [ 1, 2 ] ✓ expected ${this} to not have the same ordered members as [ 2, 1 ] ✓ expected ${this} to not have keys 'c', or 'd' ✓ expected ${this} to have keys 'a', and 'b' ✓ expected ${this} to be a string ✓ expected ${this} to include 2 ✓ expected ${this} to include 'foo' ✓ expected ${this} to equal 1 ✓ expected ${this} to be true ✓ expected ${this} to be false ✓ expected ${this} to be null ✓ expected ${this} to be undefined ✓ expected ${this} to be NaN ✓ expected ${this} to be empty ✓ expected ${this} to not be arguments ✓ expected ${this} to not equal { a: 1 } ✓ expected ${this} to have property 'length' ✓ expected ${this} to have a length of 3 got ${actual} ✓ expected ${this} to be at most 3 ✓ expected ${this} to not be an instance of Array ✓ expected ${this} to have property 'a' ✓ expected ${this} to match /^foo/ ✓ expected ${this} to contain 'bar' ✓ expected ${this} to be a function ✓ expected ${this} to throw an error ✓ expected ${this} to satisfy [Function] ✓ expected ${this} to equal 1.5 ✓ expected ${this} to have the same members as [ 2, 1, 3 ] ✓ expected ${this} to contain one of [ 'sunny', 'cloudy' ] ✓ expected ${this} to be extensible ✓ expected ${this} to be a finite number ```