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https://github.com/ssube/mocha-foam
Mocha-style wrapper for fast-check property testing
https://github.com/ssube/mocha-foam
fast-check mocha mochajs property-based-testing
Last synced: about 1 month ago
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Mocha-style wrapper for fast-check property testing
- Host: GitHub
- URL: https://github.com/ssube/mocha-foam
- Owner: ssube
- License: mit
- Created: 2021-07-21T04:40:33.000Z (over 3 years ago)
- Default Branch: master
- Last Pushed: 2024-05-22T21:43:05.000Z (6 months ago)
- Last Synced: 2024-05-22T22:41:40.585Z (6 months ago)
- Topics: fast-check, mocha, mochajs, property-based-testing
- Language: TypeScript
- Homepage:
- Size: 251 KB
- Stars: 2
- Watchers: 3
- Forks: 2
- Open Issues: 8
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE.md
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README
# mocha-foam
An experimental [Mocha BDD](https://mochajs.org/#bdd) wrapper for [fast-check's](https://github.com/dubzzz/fast-check/) property based testing.
## Contents
- [mocha-foam](#mocha-foam)
- [Contents](#contents)
- [Install](#install)
- [Usage](#usage)
- [Build](#build)
- [License](#license)
## Install
Add `mocha-foam` to your project as a dev dependency, along with `fast-check` and `mocha`, if you are not already
using them:
```shell
> yarn add -D fast-check mocha mocha-foam
```
## Usage
This is a BDD-style wrapper around `fc.check(fc.asyncProperty(...))`, and supports all of the same [Arbitraries](https://github.com/dubzzz/fast-check/blob/main/documentation/Arbitraries.md)
that fast-check normally provides.
Property based suites are defined with `over` and the library is provided as an ES module:
```typescript
import { expect } from 'chai';
import { integer } from 'fast-check';
import { over } from 'mocha-foam';
describe('example properties', () => {
over('some numbers', integer(), (it) => {
it('should be even', (n: number) => {
return n % 2 === 0;
});
it('should be odd', async (n: number) => {
expect(n % 2).to.equal(1);
});
});
});
```
Assertions can be made through `expect` (and [the other Chai assertion styles](https://www.chaijs.com/guide/styles/))
or by returning a boolean, and may be `async` functions. The test callbacks are called with a Mocha context in `this`,
so [the usual caveats](https://mochajs.org/#arrow-functions) apply to arrow functions.
Note the wrapped `it` passed to the suite callback by `over`. This wrapped `it` calls through to Mocha's `it`, after
wrapping the test in a fast-check property, while `over` calls through to Mocha's `describe`. Most Mocha features,
like `beforeEach` and `afterEach` hooks, work correctly within the suite defined by `over`.
You can pass additional parameters to the fast-check Runner after the suite callback:
```typescript
describe('more examples', () => {
over('some UUIDs', uuid(), (it) => {
// beforeEach hooks work normally, since the wrapped it calls through to real it
beforeEach(() => {
console.log('before each UUID test');
});
it('should be a good one', (id: string) => {
return id[9] !== 'a';
});
it('should be long enough', (id: string) => {
expect(id).to.have.length.greaterThan(2);
});
}, {
// fast-check parameters are supported, like examples
examples: ['a', 'b'],
numRuns: 1_000,
});
over('mapped properties', tuple(lorem(), integer()).map(([a, b]) => a.substr(b)), (it) => {
it('should have content', (text: string) => {
return text.length > 0;
});
}, {
// error formatting can be overridden with a custom handler, or fast-check's default reporter
errorReporter: defaultReportMessage,
});
});
```
The default reporter, `briefReporter`, will print the number of runs, number of shrinks, and any counterexamples
found:
```none
5) example properties
some UUIDs
should be a good one:
Error: Property failed by returning false after 3 runs and 8 shrinks, failing on: "00000000-a000-300d-8000-000000000000" (seed: -886543855, path: '2:0:10:0:10:0:2:3:3')
at /home/ssube/code/ssube/mocha-foam/out/src/index.js:20:385
at processTicksAndRejections (internal/process/task_queues.js:97:5)
```
## Build
To build `mocha-foam`, run `make`. The build depends on:
- Node 14+
- Yarn 1.x
To run small tests with coverage, run `make cover`.
The `make help` target will print help for the available targets.
## License
`mocha-foam` is released under [the MIT license](LICENSE.md).