Enforcing architecture rules with a unit test…

Posted February 24th, 2010 by Julien

… is neat!

At the beginning of a project, everybody in the team agrees to make things properly, identify layers, isolate responsibilities, code with defined formatting rules, etc. But after a few weeks, rules tend to be bent and laxism is all over the place. Formatting rules can be checked at code-time using Checkstyle Eclipse plugin, test coverage can be monitored using Maven Cobertura plugin (build-time) or EclEmma Eclispe plugin (test-time), but what can one use to enforce a certain set of architecture rules?

You use a unit test that triggers a Checkstyle “importControl” module of course! Okay, you will use the Checkstyle API, so you need the checkstyle JAR on your classpath. The unit test will initialize an audit context, referencing a configuration file that has to be on the classpath too :

public class CheckstyleIntegrationTest {

	class Listener implements AuditListener {

		public List<AuditEvent> errorList = new ArrayList<AuditEvent>();

		public void addError(AuditEvent arg0) {
			errorList.add(arg0);
		}

		public void addException(AuditEvent arg0, Throwable arg1) {
			throw new RuntimeException("Error while executing checksyle", arg1);
		}

		...

	}

	@SuppressWarnings("unchecked")
	private List<File> getList(String... directories) {
		List<File> l = new ArrayList<File>();
		for (String s : directories) {
			l.addAll(FileUtils.listFiles(new File(s), new String[] { "java" }, true));
		}
		return l;
	}

	@Test
	public void check() throws Exception {
		InputStream is = getClass().getResourceAsStream("/checkstyle.xml");
		PropertyResolver propertyResolver = new PropertyResolver() {

			public String resolve(String arg0) throws CheckstyleException {
				return null;
			}

		};
		Configuration configuration = ConfigurationLoader.loadConfiguration(is, propertyResolver, false);
		Checker checker = new Checker();
		checker.setModuleClassLoader(getClass().getClassLoader());
		checker.configure(configuration);
		Listener listener = new Listener();
		checker.addListener(listener);
		checker.process(getList("src/main/java", "src/mock/java"));
		for (AuditEvent auditEvent : listener.errorList) {
			System.err.println("Problem in file " + auditEvent.getFileName() + " : " + auditEvent.getMessage());
		}
		Assert.assertEquals(0, listener.errorList.size());
	}

}

Then in your checkstyle.xml configuration file :

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
    "-//Puppy Crawl//DTD Check Configuration 1.2//EN"
    "http://www.puppycrawl.com/dtds/configuration_1_2.dtd">

<module name="Checker">
	<module name="TreeWalker">
		<module name="ImportControl">
			<property name="file" value="src/test/resources/import-control.xml" />
		</module>
	</module>
</module>

And the only thing left is to specify your rules, for example :

<?xml version="1.0"?>
<!DOCTYPE import-control PUBLIC
    "-//Puppy Crawl//DTD Import Control 1.0//EN"
    "http://www.puppycrawl.com/dtds/import_control_1_0.dtd">

<import-control pkg="com.mycompany">
	<subpackage name="services">
		<!-- common packages -->
		<allow pkg="java" />
		<allow pkg="javax" />
		<allow pkg="org.springframework" />
		<allow pkg="org.apache.commons" />
		<allow pkg="org.apache.log4j" />

		<!-- application layers -->
		<allow pkg="com.mycompany.dao" />
		<allow pkg="com.mycompany.model" />

etc ....