JUnit is the glue that holds many open source projects together. But JUnit has problems performing multithreaded unit tests. This creates considerable difficulty for middleware developers in the open source J2EE market. This article introduces GroboUtils, a JUnit extension library designed to address this problem and enable multithreaded unit testing in JUnit. A basic understanding of JUnit and threads is recommended but not necessary for readers of this article.
Introduction
If you've worked on open source Java projects or read the multitude of books on "Extreme Programming" and other rapid-development models, then you've likely heard about JUnit. Written by Erich Gamma and Kent Beck, JUnit is an automated testing framework for Java. It allows you to define "unit tests" for your software -- programs that test whether or not the code is functioning properly, usually on a method-by-method basis.
JUnit can help your development team in many ways -- too many to cover in one article. But from one developer to another, JUnit truly excels at two things:
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It forces you to use your own code. Your tests function as client code for your production code. Getting to know your software from the client's perspective can help you identify problems in the API and improve how the code will eventually get used.
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It gives you confidence to make changes in your software. You'll know right away if you've broken the test cases. At the end of the day, if the light is green, the code is clean. Check it in with confidence.
But JUnit is no silver bullet. Third-party extension libraries such as HttpUnit, JWebUnit, XMLUnit, and a host of others have risen to address perceived holes in the framework by adding functionality. One of the areas JUnit doesn't cover is multithreaded unit tests.
In this article, we're going to look at a little-known extension library that solves this problem. We'll start by setting up the JUnit framework and running an example to show poor use of threads in testing. After we've identified the obstacles of threaded testing, we'll walk through an example using the GroboUtils framework.
Threads in Review
For those of you new to threads, it's all right to panic a bit at this point -- just don't overdo it. Get it out of your system. We're going to take a fifty-thousand-foot view of threads. Threads allow your software to multitask -- that is, do two things at the same time.
In their book A Programmer's Guide to Java Certification, Khalid Mugal and Rolf Rasmussen briefly describe threads as follows:
"A thread is a path of execution within a program, that is executed separately. At runtime, threads in a program have a common memory space and can therefore share data and code; i.e., they are lightweight. They also share the process running the program.
Java threads make the runtime environment asynchronous, allowing different tasks to be performed concurrently." (p.272)
In web applications, many users can send requests to your software at the same time. When writing unit tests to stress your code, you need to simulate that sort of concurrent traffic. This is especially true if you're trying to develop robust middleware components. Threaded tests would be ideal for these components.
