@fast-check/ava

@fast-check/ava

Bring the power of property based testing framework fast-check into AVA. @fast-check/ava simplifies the integration of fast-check into AVA testing framework.

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Getting Started

Install @fast-check/ava:

npm install --save-dev @fast-check/ava

In order to work properly, @fast-check/ava requires ava to be installed.

Example

import { testProp, fc } from '@fast-check/ava';

// for all a, b, c strings
// b is a substring of a + b + c
testProp('should detect the substring', [fc.string(), fc.string(), fc.string()], (t, a, b, c) => {
  t.true((a + b + c).includes(b));
});

The property is passed AVA's t argument as its first parameter, and the value of each arbitrary for the current test case for the rest of the parameters.

@fast-check/ava supports all of AVA's assertions and like AVA, it supports synchronous and asynchronous functions, including promises, observables, and callbacks. See AVA's documentation for more information.

Advanced

fast-check Parameters

testProp accepts an optional fc.Parameters for forwarding custom parameters to fast-check (more).

import { testProp, fc } from '@fast-check/ava';

testProp(
  'should detect the substring',
  [fc.string(), fc.string(), fc.string()],
  (t, a, b, c) => {
    t.true((a + b + c).includes(b));
  },
  { numRuns: 10 } // Example of parameters
);

AVA Modifiers

@fast-check/ava also comes with .only, .serial .skip, and .failing modifiers from AVA.

import { testProp, fc } from '@fast-check/ava';

testProp(
  'should replay the test for the seed 4242',
  [fc.nat(), fc.nat()],
  (t, a, b) => {
    t.is(a + b, b + a);
  },
  { seed: 4242 }
);

testProp.skip('should be skipped', [fc.fullUnicodeString()], (t, text) => {
  t.is([...text].length, text.length);
});

AVA before/after Hooks

@fast-check/ava exposes AVA's before/after hooks:

import { testProp, fc } from '@fast-check/ava';

testProp.before((t) => {
  connectToDatabase();
});

testProp();
// ... omitted for brevity

testProp.after((t) => {
  closeDatabaseConnection();
});

AVA Execution Context

@fast-check/ava mirror's AVA's procedure for customizing the test execution context:

import { fc, testProp as anyTestProp, PropertyTestInterface } from '@fast-check/ava';

type TestContext = {
  state: string;
};

const testProp = anyTestProp as PropertyTestInterface<TestContext>;

testProp('should reach terminal state', [fc.string()], (t, received) => {
  // here t is typed as ExecutionContext<TestContext>
  console.log(t.context.state); // logs 'uninitialized'
  // ... omitted for brevity
});

Minimal requirements

@fast-check/ava	AVA	fast-check
^1.0.0	>=4.0.0	^3.0.0