Global settings

Share settings cross runners.

Per test settings

By default, the runners take an optional argument for extra settings. Some of these settings can be re-used over-and-over in the same file and across several files.

Example:

test('test #1', () => {
  fc.assert(myProp1, { numRuns: 10 });
});
test('test #2', () => {
  fc.assert(myProp2, { numRuns: 10 });
});
test('test #3', () => {
  fc.assert(myProp3, { numRuns: 10 });
});

Shared settings

The recommended way to share settings across runners is to use configureGlobal.

Here is how to update the snippet above to share the settings:

fc.configureGlobal({ numRuns: 10 });

test('test #1', () => {
  fc.assert(myProp1);
});
test('test #2', () => {
  fc.assert(myProp2);
});
test('test #3', () => {
  fc.assert(myProp3);
});

warning

configureGlobal fully resets the settings. In other words, it fully drops the previously defined global settings if any even if they applied on other keys.

:::tip Enrich existing global settings If you want to only add new options on top of the existing ones you may want to use readConfigureGlobal as follow:

fc.configureGlobal({ ...fc.readConfigureGlobal(), ...myNewOptions });

You can also fully reset all the global options by calling resetConfigureGlobal. :::

Resources: API reference.
Available since 1.18.0.

Integration with test frameworks

Main test frameworks provide ways to connect configureGlobal on all the spec files without having to copy the snippet over-and-over. This section describes how to do so with some of them.

Jest

You need to define a setup file (if not already done):

jest.config.js

module.exports = {
  setupFiles: ['./jest.setup.js'],
};

Then you can add the global settings snippet directly into the setup file:

jest.setup.js

const fc = require('fast-check');
fc.configureGlobal({ numRuns: 10 });

Mocha

When calling mocha, you can provide an additional parameter to specify a file to be executed before the code of your tests by adding --file=mocha.setup.js.

Then you can add the global settings snippet directly into the setup file:

mocha.setup.js

const fc = require('fast-check');
fc.configureGlobal({ numRuns: 10 });

Vitest

You need to define a setup file (if not already done):

vitest.config.js

import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    // ...
    setupFiles: ['./vitest.setup.js'],
  },
});

Then you can add the global settings snippet directly into the setup file:

vitest.setup.js

import fc from 'fast-check';
fc.configureGlobal({ numRuns: 10 });