Mobile Test Engineering – Odo

at June 26th, 2014

Earlier this year we told you about Odo, an innovative mobile test engineering tool we developed here at Groupon to overcome some of the challenges involved in testing our mobile app, which more than 80 million people have downloaded worldwide. We’re excited to tell you that Odo is now available at our Groupon Github home!

The struggle is real

Our engineering teams had to come up with a way to build the engaging mobile experiences fast to our end users. Along the way, our Mobile Test Engineering team started to come across common problems in the space and we were not able to find a solution outside that would fit our needs. Specifically, we attempted to tackle some of these challenges:

  1. Development and testing of new features without dependent service API’s being available yet.
  2. We gravitated towards using realistic data, but needed more than a traditional mock server. While a mock may work, you will need to update the stub data whenever the service changes. In a SOA world, the maintenance can come at a huge cost.
  3. We needed a mock server that has an HTTP based interface so we can integrate with our end to end test suites as well as a mock server that could easily integrate into development builds. We wanted to be able share the manipulated data corpus across dev and test. What’s the point in reinventing the wheel, right?
  4. We had to simulate a complex scenario that may not be possible using static data. Example: three requests are made to an API. The first two are successful, but the third fails.

Oh boy! It’s Odo!

Odo is a man-in-the-middle for client and server communication. It can easily be used as a mock/stub server or as a proxy server. Odo is used to modify the data as it passes through the proxy server to simulate a condition needed for test. For example, we can request a list of Groupon deals and set the “sold out” condition to true to verify our app is displaying a sold out deal correctly. This allows us to still preserve the state of the original deal data that other developers and testers may be relying on.

The behaviors within Odo are configurable through a REST API and additional overrides can be added through plugins, so Odo is dynamic and flexible. A tester can manually change the override behaviors for a request, or configurations can even be changed at runtime from within an automated test.

Odo In A Nutshell

As a request passes through Odo, the request’s destination host and URI are matched against the hosts and paths defined by the configuration. If a request matches a defined source host, the request is updated with the destination host. If the host name doesn’t match, the requests is sent along to its original destination. If the URI does not match a defined path, the request is executed for its new host. If the host and path match an enabled path, the enabled overrides are applied during its execution phase. There are two different types of overrides in Odo.

A Request Override is an override applied to a request coming from the mobile client on its way to the server. Generally, an override here will be for adding/editing a parameter or modifying request headers.

A Response Override executes on the data received from the server before passing data back to the client. This is where we can mock an API endpoint, change the HTTP response code, modify the response data to simulate a “sold out” Groupon deal, change the price, etc.

Automation Example

Client client = new Client(“API Profile", false);
client.setCustomResponse("Global", "response text”);
client.addMethodToResponseOverride("Global”, "com.groupon.proxy.internal.Common.delay");
client.setMethodArguments("Global", "com.groupon.proxy.internal.Common.delay", 1, 100);

In this example, we are applying a custom response (stub) with value “response text” to a path defined with a friendly name “Global”. Then we add a 100ms delay to that same path. Go nuts! Try adding a 10 second delay to simulate the effects of network latency on your app.


Odo brings benefits to several different areas of development:

  • Test automation owners can avoid stub data maintenance, and tests gain the ability to dynamically configure Odo to simulate complex or edge-case scenarios.

  • Manual Testers gain the same ability to configure Odo through the UI. No coding knowledge is required.

  • Developers can use Odo to avoid dependency blocks. If a feature depends on an API currently in development, Odo can be used to simulate the missing component and unblock development.

  • Multiple client support. With this feature, a single Odo instance can be run, but have different behaviors for each client connected. This allows a team to run a central Odo instance, and the team members can modify Odo behavior without affecting other members’ configurations.

Broader Odo Adoption

With Odo’s flexibility, our Test Engineering teams adopted the usage of it for testing our interaction tier applications built on Node.js (you know, the ones powering the frontend of We even have an internal fork that scales so we can use it as part of our capacity testing efforts. We’ll push that update in the near future as well.

Simple as 1-2-3

Our Github page provides some getting started instructions to get you up and running quickly. All you need is Java(7+) and odo.war from our release. There is a sample to give you an idea of how to apply everything Odo has to offer to your projects.


Github –

Readme –

Download –

Community Collaboration

We have a roadmap of new features we’ll be adding to Odo over time. We’d love your feedback and contribution towards making Odo a great project for everyone.

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