# Getting Started with Snippets for Mobly

Mobly Snippet Lib is a library for triggering device-side code from host-side
[Mobly](http://github.com/google/mobly) tests. This tutorial teaches you how to
use the snippet lib to trigger custom device-side actions.

Note: Mobly and the snippet lib are not official Google products.


## Prerequisites

-   These examples and tutorials assume basic familiarity with the Mobly
    framework, so please follow the
    [Mobly tutorial](http://github.com/google/mobly) before doing this one.
-   You should know how to create an Android app and build it with gradle. If
    not, follow the
    [Android app tutorial](https://developer.android.com/training/basics/firstapp/index.html).


## Overview

The Mobly Snippet Lib allows you to write Java methods that run on Android
devices, and trigger the methods from inside a Mobly test case. The Java methods
invoked this way are called `snippets`.

The `snippet` code can either be written in its own standalone apk, or as a
[product flavor](https://developer.android.com/studio/build/build-variants.html#product-flavors)
of an existing apk. This allows you to write snippets that instrument or
automate another app.

Under the hood, the snippet lib starts a web server which listens for requests
to trigger snippets. It locates the corrsponding methods by reflection, runs
them, and returns results over the tcp socket. All common built-in variable
types are supported as arguments.


## Usage

The [examples/](examples/) folder contains examples of how to use the
mobly snippet lib along with detailed tutorials.

*   [ex1_standalone_app](examples/ex1_standalone_app): Basic example of a
    snippet which is compiled into its own standalone apk.
*   [ex2_espresso](examples/ex2_espresso): Example of a snippet which
    instruments a main app to drive its UI using
    [Espresso](https://google.github.io/android-testing-support-library/docs/espresso/).