### [percy-nightmare on GitHub <i class="fa fa-github" aria-hidden="true"></i>](🔗)

[](🔗)

Visual regression testing for [Nightmare](🔗) tests with Percy.

# Installation

📘



Make sure you have completed [Setup](🔗) of your CI service first. You can also test Percy in your [local development](🔗) environment.

Install `@percy/nightmare` using `npm`:

Or using `yarn`:

# Quick Setup

These are the minimal steps required to add visual testing to your existing Nightmare tests:

1. Import `percySnapshot()` into your test file: `const { percySnapshot } = require('@percy/nightmare')`

2. Call `nightmare.use(percySnapshot(<snapshotName>))` from your tests wherever you want to save a snapshot.

3. Wrap your test run command in `percy exec --`, e.g. `percy exec -- mocha`.

Next, we will go through each of these steps in detail.

# Setup

In order to start creating snapshots from your Nightmare tests, you'll need to import the `percySnapshot()` function from the `@percy/nightmare` package. You will need to do this in each test file from which you want to take snapshots:

You will then use `percySnapshot(...)` inside a `nightmare.use(...)` statement:

Finally, wrap your test runner command in the `percy exec` command. This will start a Percy agent to receive snapshots from your tests and upload them to your Percy dashboard. For example, if you are using [Mocha](🔗) for your tests, your new test command becomes:

Note the double dash, `--`, between `percy exec` and your test run command.

That's it! Now, whenever CI runs, a snapshot of the app in that state will be uploaded to Percy for visual regression testing!

For an example showing how to add Percy snapshots to an existing Nightmare test suite, see [https://github.com/percy/example-percy-nightmare/pull/6](🔗).

# Usage

`snapshotName` is a required string that will be used as the snapshot name. It can be any string that makes sense to you to identify the page state. It should be unique and remain the same across builds. For more details on generating snapshot names, see [Autogenerated snapshot names](🔗).

`options` is an optional hash that can include:

• `widths`: An array of integers representing the browser widths at which you want to take snapshots.

• `minHeight`: An integer specifying the minimum height of the resulting snapshot, in pixels. Defaults to 1024px.

## Examples

# Global Configuration

You can also configure Percy to use the same options over all snapshots. To see supported configuration including widths read our [Configuration doc](🔗).

# Contributing

1. Fork it ( https://github.com/percy/percy-nightmare/fork )

2. Create your feature branch (`git checkout -b my-new-feature`)

3. Commit your changes (`git commit -am 'Add some feature'`)

4. Push to the branch (`git push origin my-new-feature`)

5. Create a new pull request

[Throw a ★ on it!](🔗) 😄