@stryker-mutator/typescript
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A plugin for TypeScript-based projects using Stryker
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# Stryker Typescript
A collection of plugins for native TypeScript support in [Stryker](https://stryker-mutator.io), the ~~JavaScript~~ *TypeScript* Mutation testing framework.
## Quickstart
First, install Stryker itself (you can follow the [quickstart on the website](https://stryker-mutator.io/quickstart.html))
Next, install this package:
```bash
npm install --save-dev @stryker-mutator/typescript
```
Now open up your `stryker.conf.js` (or `stryker.conf.json`) file and add the following components:
```javascript
coverageAnalysis: 'perTest', // Coverage analysis is supported
tsconfigFile: 'tsconfig.json', // Location of your tsconfig.json file
mutator: 'typescript', // Specify that you want to mutate typescript code
transpilers: [
'typescript' // Specify that your typescript code needs to be transpiled before tests can be run. Not needed if you're using ts-node Just-in-time compilation.
]
```
Now give it a go:
```bash
$ stryker run
```
## Peer dependencies
The `@stryker-mutator/typescript` package is collection a plugins for `stryker` to enable `typescript` support. As such, you should make sure you have the correct versions of its dependencies installed:
* `typescript`
* `@stryker-mutator/core`
For the current versions, see the `peerDependencies` section in the [package.json](https://github.com/stryker-mutator/stryker/blob/master/packages/typescript/package.json).
These are marked as `peerDependencies` so you get a warning during installation when the correct versions are not installed.
## Load the plugins
In order to use one of the `@stryker-mutator/typescript`'s plugins it must be loaded into Stryker.
The easiest way to achieve this, is *not have a `plugins` section* in your config file. That way, all `node_modules` starting with `stryker-` will be loaded.
If you do decide to choose specific modules, don't forget to add `'@stryker-mutator/typescript'` to the list of plugins to load.
## 3 Plugins
This package contains 3 plugins to support TypeScript
1. [TypescriptOptionsEditor](#typescriptoptionseditor)
1. [TypescriptMutator](#typescriptmutator)
1. [TypescriptTranspiler](#typescripttranspiler)
### TypescriptOptionsEditor
The `TypescriptOptionsEditor` is a handy plugin that reads **your** tsconfig.json file and loads it into stryker.conf.js. It will capture all your tsconfig settings to the `tsconfig` in stryker (this property is later used by the `TypescriptMutator` and the `TypescriptTranspiler`)
Enable the config editor by pointing the `tsconfigFile` property to your tsconfig location:
```javascript
// stryker.conf.js
{
tsconfigFile: 'tsconfig.json',
}
```
We always override some properties to enforce these rules (see [issue 391](https://github.com/stryker-mutator/stryker/issues/391) to find out why):
```js
allowUnreachableCode: true
noUnusedLocals: false
noUnusedParameters: false
```
### TypescriptMutator
The `TypescriptMutator` is a plugin to mutate typescript code. It builds a Typescript [Abstract Syntax Tree (AST)](https://en.wikipedia.org/wiki/Abstract_syntax_tree) and mutates your code using different kind of mutators.
See [test code](https://github.com/stryker-mutator/stryker/tree/master/packages/typescript/test/unit/mutator) to know which mutations are supported.
Configure the Typescript mutator in your `stryker.conf.js` (or `stryker.conf.json`) file:
```javascript
// stryker.conf.js
{
mutator: 'typescript'
}
```
### TypescriptTranspiler
The `TypescriptTranspiler` is a plugin to transpile typescript source code before running tests. If you're using a bundler you might want to configure that instead.
Given your Typescript configuration (see **TypescriptOptionsEditor**) it generates the javascript output. This is also used to transpile each mutant to javascript. Internally, it uses the same method as Typescript's watch mode (`tsc -w`), so it can transpile mutants fairly efficiently.
Configure the Typescript transpiler in your `stryker.conf.js` (or `stryker.conf.json`) file:
```javascript
// stryker.conf.js
{
transpilers: [
'typescript'
// You can specify more transpilers if needed
]
}
```