https://github.com/nighttrax/strictly-chai

A statically typed subset of chai assertions
https://github.com/nighttrax/strictly-chai

assert bdd chai testing typescript

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A statically typed subset of chai assertions

• Host: GitHub
• URL: https://github.com/nighttrax/strictly-chai
• Owner: NiGhTTraX
• Created: 2018-05-06T10:09:30.000Z (over 6 years ago)
• Default Branch: master
• Last Pushed: 2018-09-12T05:06:22.000Z (about 6 years ago)
• Last Synced: 2024-09-15T15:11:39.092Z (about 2 months ago)
• Topics: assert, bdd, chai, testing, typescript
• Language: TypeScript
• Homepage:
• Size: 975 KB
• Stars: 0
• Watchers: 3
• Forks: 0
• Open Issues: 10
• Metadata Files:
  • Readme: README.md

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README

        
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> A statically typed subset of [chai](http://www.chaijs.com) assertions written

in TypeScript.

## Usage

![object-contains](./docs/object-contains.png)

![demo](./docs/demo.gif)

This library exports a subset of chai's [BDD API](http://www.chaijs.com/api/bdd/)

so check out their docs on usage. The only difference is that the `.equal`

assertion is by default deep (equivalent to `.deep.equal`).

## Philosophy

```js

expect(new Set([1, 2])).to.contain('a');

```

While the above is perfectly valid JS and chai will throw an AssertionError at

runtime, it was this author's desire to turn that into a compile time error when

using TypeScript.

Using this library instead of `chai.expect` in the assertion above will

fail to compile with the following:

```

TS2345: Argument of type '"a"' is not assignable to parameter of type 'number'.

```

## But wait, what about `@types/chai`?

`@types/chai` declares most arguments as `any` so using chai directly in

TypeScript will not provide meaningful type checking.

Could this library export stricter types to be used in place of `@types/chai`,

instead of also providing a "re-implementation" (the current implementation is

a drop-in replacement) of chai? Perhaps, but the real strength of this library

is the ability to extend it for new types - see below for details.

## Plugins

You can extend this library, similarly to how `chai.use` works, and keep type

safety using `extend`:

```ts

import { extend, Expect, IsType, Plugin } from 'strictly-chai/extend';

type MyAwesomeType = {

  myAwesomeProp: 42

};

interface MyAwesomeAssertion {

  to: {

    be: {

      awesome: (expected: number) => void;

    }

  }

}

const isMyAwesomeType: IsType = (actual: any): actual is MyAwesomeType =>

  ((actual as MyAwesomeType).myAwesomeProp === 42);

const plugin: Plugin = chai => {

  // You have access to the chai instance so you can do chai.use() here.

  const myAwesomeExpect: Expect = actual => ({

    to: {

      be: {

        awesome: () => {}

      }

    }

  });

  return {

    isType: isMyAwesomeType,

    expect: myAwesomeExpect

  };

};

const expect = extend(plugin);

// This is our awesome assertion.

expect({ myAwesomeProp: 42 }).to.be.awesome(23);

// TS2345: Argument of type '"foo"' is not assignable to parameter of type 'number'.

expect({ myAwesomeProp: 42 }).to.be.awesome('foo');

// This is from the inherited base assertions.

expect('foobar').to.contain('foo');

```