# @studyportals/cypress-slicer

> Slices the Cypress tests resolved by the `specPattern` config property into multiple chunks and runs them in parallel.

```shell
# runs only the first third (natural sorting) of the tests
npx cypress run --env workers=3,worker=1

# runs only the the last third (natural sorting) of the tests
npx cypress run --env workers=3,worker=3

# runs only all the tests
npx cypress run --env workers=1,worker=1

npx cypress run
```

## Install

Assuming you have Cypress installed, add this module as a dev dependency.

```shell
# using NPM
npm i -D @studyportals/cypress-slicer
# using Yarn
yarn add -D @studyportals/cypress-slicer
```

**Note**: @studyportals/cypress-slicer only works with Cypress version >= 10.


### Config file

**optional:** load and register this module from the [config file](https://docs.cypress.io/guides/references/configuration#setupNodeEvents):

```js
// cypress.config.js
{
  e2e: {
    setupNodeEvents(on, config) {
      require('@studyportals/cypress-slicer/plugin')(config);
      return config;
  },
  }
}
```
## Usage Overview

The number of chunks is determined by the `workers` environment variable. The `worker` environment variable determines which chunk to run.


You can configure the number of `workers` and the `worker` index through the `env` property of the configuration defined  in the `cypress.config.js` file:
```js
{
  env: {
    workers: process.env.WORKERS,
    worker: process.env.WORKER,
  }
}
```
> ⚠ The `worker` index is 1-based, not 0-based.