k6Chai configuration

Chai exposes a number of configuration options that can change how the library behaves.

Config option	Default	Description
truncateMsgThreshold	300	Check message length is truncated to this value.
truncateVariableThreshold	100	Variables interpolated into check message are truncated to this length.
aggregateChecks	true	The actual values are not interpolated into the check message. Disable for tests with 1 iteration.
logFailures	false	When the check fails, debug messages are printed.

truncateMsgThreshold configuration variable sets the upper bound for how large the full check message can be. truncateVariableThreshold sets the upper bound for how large an individual variable can be. It is intended as a safeguard from mistakes when a very large string is included in the check name, especially when the aggregateChecks is set to false;.

import http from 'k6/http';
import { describe, expect, chai } from 'https://jslib.k6.io/k6chaijs/4.3.4.1/index.js';

// individual variables should be up to 20 chars after rendering.
chai.config.truncateVariableThreshold = 20;

// whole check() message must be below 300 chars.
chai.config.truncateMsgThreshold = 300;

// the variable values (resp.status) are inserted into the check message - useful for debugging or tests with 1 iteration
chai.config.aggregateChecks = false;

// when the check fails, WARN messages with variables are printed. Useful for debugging.
chai.config.logFailures = true;

export default function testSuite() {
  describe('Testing bad assertion.', () => {
    const response = http.get('https://test-api.k6.io/');

    expect(response.body).to.have.lengthOf.at.least(500);
  });
}

The resulting

█ Testing bad assertion.
  ✓ expected '<!DOCTYPE html>\n<html lang="en">\n<hea...' to have property 'length'
  ✓ expected '<!DOCTYPE html>\n<html lang="en">\n<hea...' to have a length at least 500 got 15714

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