https://github.com/nmuldavin/chai-almost

Extends Chai with assertions that allow for floating point rounding errors
https://github.com/nmuldavin/chai-almost

approximation assertion-library assertions chai chai-assertions chai-plugin deep-equals javascript mocha rounding-error testing testing-tools

Last synced: about 2 months ago
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Extends Chai with assertions that allow for floating point rounding errors

• Host: GitHub
• URL: https://github.com/nmuldavin/chai-almost
• Owner: nmuldavin
• Created: 2017-05-13T00:39:29.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2019-03-17T04:57:29.000Z (almost 6 years ago)
• Last Synced: 2024-10-11T14:38:40.494Z (3 months ago)
• Topics: approximation, assertion-library, assertions, chai, chai-assertions, chai-plugin, deep-equals, javascript, mocha, rounding-error, testing, testing-tools
• Language: JavaScript
• Size: 40 KB
• Stars: 4
• Watchers: 1
• Forks: 1
• Open Issues: 3
• Metadata Files:
  • Readme: README.md

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README

        
# chai-almost

[![travis](https://travis-ci.org/nmuldavin/chai-almost.svg?branch=master)](https://travis-ci.org/nmuldavin/chai-almost)

[![npm](https://img.shields.io/npm/v/chai-almost.svg)](https://www.npmjs.com/package/chai-almost)

[![node](https://img.shields.io/badge/node-%3E=0.10-green.svg)](https://www.npmjs.com/package/chai-almost)

Extends [chai](https://github.com/chaijs/chai) with assertions that allow numbers to be "almost" equal (as in, within some tolerance of one another). This is useful in particular when accounting for floating point rounding errors or other approximations.

## Installation

```

npm install chai-almost --save-dev

```

## Use

To use, import the module then invoke it with `chai.use`:

```

const chai = require('chai');

const chaiAlmost = require('chai-almost');

chai.use(chaiAlmost());

```

By default, `chai-almost` allows a tolerance of 1 x 10-6. This will let most rounding errors pass safely but will still reject most true inequalities. You may override this value by passing your desired tolerance as an argument to the module on invocation:

```

chai.use(chaiAlmost(0.1));

```

### Assertions

The `almost` assertion may be used chainably with deep or shallow equality:

```

// shallow

expect(3.9999999).to.almost.equal(4);	        // passes

expect(3.9).to.almost.equal(4);			// fails

expect(4.0000001).to.be.almost(4);		// passes

expect(4.1).to.not.be.almost(4);		// passes

// deep

expect({ taco: 'pastor', num: 3.9999999 }).to.almost.eql({ taco: 'pastor', num: 4 }); // passes

expect([[1, 2, 2.9999999], 1.0000001]).to.be.deep.almost([[1, 2, 3], 1]);             // passes

expect({ taco: 'pastor', num: 3.9 }).to.not.almost.eql({ taco: 'pastor', num: 4 });   // passes

```

Equality checks on non-numbers are left unchanged:

```

expect('taco').to.almost.equal('taco');   // still passes

expect({ x: 5 }).to.be.almost({ x: 5 });  // still fails (shallow equality)

expect(['tacos', 2, 3]).to.be.deep.almost(['burritos', 2, 2.9999999]); // still fails

```

### Specific tolerance

A single-instance custom tolerance for shallow or deep equality may be passed in as the second argument to `almost`:

```

expect(10).to.be.almost(15, 10)                   // passes

expect([4, 2, 5]).to.be.deep.almost([3, 4, 7], 3) // passes

```