gemini/doc/plugins.md

UI Screenshot testing utility

# Writing plugins

Gemini plugin is just an npm package with a `gemini-<plugin name>` name.
Module should export a single function which receives `Gemini` class instance
and user-specified options.
`Gemini` instance contains two fields:
* `config` — current config with specified options
* `events` — all emitted events, which can be used by plugins

For example:
```js
module.exports = function(gemini, options) {
    console.log('Hello from plugin');
    console.log('Show me config: ', gemini.config);
    console.log('Show me all events: ', gemini.events);
};
```

Documentation on the `gemini` object can be found in [programmatic
API](programmatic-api.md) document.

Options are specified by a user in a config file and passed to the plugin as
is. For example:

.gemini.yml:
```yaml
system:
  plugins:
    greeter:
      name: Mr. Incredible
```

Plugin:
```javascript
module.exports = function(gemini, options) {
    console.log('Hello, %s' options.name);
};

```

When publishing plugins, add `gemini-plugin` keyword to your `package.json` to
help users discovering it.