How do I unit test a custom ant task?

Question

I am writing a custom ant task that extends Task. I am using the log() method in the task. What I want to do is use a unit test while deveoping the task, but I don't know how to set up a context for the task to run in to initialise the task as if it were running in ant.

This is the custom Task:

public class CopyAndSetPropertiesForFiles extends Task {
    public void execute() throws BuildException {
     log("CopyAndSetPropertiesForFiles begin execute()");

     log("CopyAndSetPropertiesForFiles end execute()");
    }
}

This is the unit test code:

CopyAndSetPropertiesForFiles task = new CopyAndSetPropertiesForFiles();
task.execute();

When the code is run as a test it gives a NullPointerException when it calls log.

java.lang.NullPointerException
    at org.apache.tools.ant.Task.log(Task.java:346)
    at org.apache.tools.ant.Task.log(Task.java:334)
    at uk.co.tbp.ant.custom.CopyAndSetPropertiesForFiles.execute(CopyAndSetPropertiesForFiles.java:40)
    at uk.co.tbp.ant.custom.test.TestCopyAndSetPropertiesForFiles.testCopyAndSetPropertiesForFiles(TestCopyAndSetPropertiesForFiles.java:22)

Does anybody know a way to provide a context or stubs or something similar to the task?

Thanks,

Rob.

Accepted answer from Abarax. I was able to call task.setProject(new Project()); The code now executes OK (except no logging appears in th console - at least I can exercise the code :-) ).

Answer 1

Looking at the Ant source code these are the two relevent classes: ProjectComponent and Task

You are calling the log method from Task:

public void log(String msg) {
     log(msg, Project.MSG_INFO);
}

Which calls:

public void log(String msg, int msgLevel) {
  if (getProject() != null) {
    getProject().log(this, msg, msgLevel);
  } else {
    super.log(msg, msgLevel);
  }
}

Since you do not have project set it will call "super.log(msg, msgLevel)"

public void log(String msg, int msgLevel) {
  if (getProject() != null) {
     getProject().log(msg, msgLevel);
  } else {
    // 'reasonable' default, if the component is used without
    // a Project ( for example as a standalone Bean ).
    // Most ant components can be used this way.
    if (msgLevel <= Project.MSG_INFO) {
      System.err.println(msg);
    }
  }
}

It looks like this may be your problem. Your task needs a project context.

Answer 2

Or better yet, decouple the task object itself from the logic (lets call it TaskImpl) inside the task - so that you can pass in your own dependencies (e.g., the logger). Then, instead of testing the task object, you test TaskImpl -> which you can pass in the logger, and any other weird bits and pieces it might need to do its job. Then unit testing is a matter of mocking the dependencies.

Answer 3

Ant has a handy class called BuildFileTest that extends the JUnit TestCase class. You can use it to test the behaviour of individual targets in a build file. Using this would take care of all the annoying context.

There's a Test The Task chapter in the Apache Ant Writing Tasks Tutorial that describes this.