Bug: 213332752

Clone this repo:
  1. 23cff8e Upgrade mobly-snippet-lib to 3c705915cad43acd88a8815b3f3e3cf9455a60a4 by Ziwei Zhang · 6 weeks ago main master
  2. 3c70591 Support handling data type Byte in snippet method return values by Minghao Li · 2 months ago upstream-master
  3. a3065d9 Fix the bug when using array types in snippet method arguments by Minghao Li · 2 months ago
  4. eb6ceb9 Align the behavior of returning Byte[] and returning byte[] by Minghao Li · 2 months ago
  5. 1e12206 Support using array types in snippet method arguments. by Minghao Li · 2 months ago

Getting Started with Snippets for Mobly

Mobly Snippet Lib is a library for triggering device-side code from host-side 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.


  • These examples and tutorials assume basic familiarity with the Mobly framework, so please follow the Mobly tutorial 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.


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 of an existing apk. This allows you to write snippets that instrument or automate another app.

Under The Hood

A snippet is launched by an am instrument call. Snippets use a custom InstrumentationTestRunner derived from AndroidJUnitRunner. This allows for snippets that interact with a main app‘s classes, such as Espresso snippets, and allows you to get either the test app’s or the main app's context from InstrumentationRegistry.

Once started, the special runner starts a web server which listens for requests to trigger snippets. The server's handler locates the corresponding methods by reflection, runs them, and returns results over the TCP socket. All common built-in variable types are supported as arguments.


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

  • ex1_standalone_app: Basic example of a snippet which is compiled into its own standalone apk.
  • ex2_espresso: Example of a snippet which instruments a primary app to drive its UI using Espresso.
  • ex3_async_event: Example of how to use the @AsyncRpc annotation to handle asynchronous callbacks.
  • ex4_uiautomator: Example of how to create snippets that automate the UI actions using UIAutomator. Unlike Espresso UIAutomator works even without access to app source code.
  • ex5_schedule_rpc: Example of how to use the ‘scheduleRpc’ RPC to execute another RPC at a later time, potentially after device disconnection.
  • ex6_complex_type_conversion: Example of how to pass a non-primitive type to the Rpc methods and return non-primitive type from Rpc methods by supplying a type converter.