Testing is useful but it can be very time-consuming. We have to write the test and then maintain them. It would be nice if we also had some automatic way of testing.

Static analysis is what we're looking for. It is another powerful technique that can be used anytime for achieving high quality of rules. The rules are analyzed by a specialized program without actually running it. It can be applied to any rules without any initial investments.

Drools comes with a module called drools-verifier that uses rules to analyze rules. This module can be used standalone (through API or as an ant task) or it is also included in Guvnor under QA | Analysis. Analysis can be started by clicking on the Run analysis button. The results are shown in the following screenshot:

Figure 6: Analyzing a package

Drools-verifier module analyzes rules in a package and creates a report with errors, warnings, and notes. Furthermore, it provides various other information about rules (for example, field usages by fact type and so on). The errors section represent significant problems often resulting in the rules not being able to compile. Warnings and notes highlight potential problems with rules (for example, a redundant rule that is already covered by another rule). The Drools-verifier module gives us an interesting tool to look at rules from a different perspective.