Book Image

Drools JBoss Rules 5.X Developer's Guide

By : Michal Bali
Book Image

Drools JBoss Rules 5.X Developer's Guide

By: Michal Bali

Overview of this book

<p>Writing business rules has always been a challenging task. Business rules tend to change often leading to a maintenance nightmare. This book shows you various ways to code your business rules using Drools, the open source Business Rules Management System.<br /><br />Drools JBoss Rules 5.X Developer's Guide shows various features of the Drools platform by walking the reader through several real-world examples. Each chapter elaborates on different aspects of the Drools platform. The reader will also learn about the inner workings of Drools and its implementation of the Rete algorithm.<br /><br />The book starts with explaining rule basics, then builds on this information by going through various areas like human readable rules, rules for validation, and stateful rules, using examples from the banking domain. A loan approval process example shows the use of the jBPM module. Parts of a banking fraud detection system are implemented with the Drools Fusion module which is the complex event processing part of Drools. Finally, more technical details are shown detailing the inner workings of Drools, the implementation of the ReteOO algorithm, indexing, node sharing, and partitioning.</p>
Table of Contents (22 chapters)
Drools JBoss Rules 5.X Developer's Guide
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Setting Up the Development Environment
Creating Custom Operators
Dependencies of Sample Application
Index

Writing unit tests for rules


By definition a unit in a unit test is the smallest testable part of an application; in our case it's a rule. Writing a unit test for every rule is expensive. It effectively doubles the cost of writing a rule. However, it is worth the effort. To minimize this cost we should focus on each rule in isolation. This includes isolating all external factors such as calls to services, repositories, and so on. Any mocking library can be used for this purpose.

Note

A mocking library can create a dummy implementation (a mock) of a service that we can use for testing the rules. The mock can record methods that have been called and return predefined values. We can verify that the correct method was executed an expected amount of times with the correct set of arguments. In the previous chapters jMock was used, but easyMock or mockito are also good alternatives.

By isolating all external factors, our unit tests will work even if they change. For example, the implementation of...