Java - Unit Test

java, junit, unit-testing

Solution

This method can't be tested via a unit test but only via an integration test. To make a unit test you could do a small refactor. Introduce a new interface `ProcessBuilderFactory` (and a default implementation) and inject it on your class.

public interface ProcessBuilderFactory {
    ProcessBuilder createProcessBuilder(String command);
}

public class DefaultProcessBuilderFactory implements ProcessBuilderFactory {
    public ProcessBuilder createProcessBuilder(String command) {
        return new ProcessBuilder(command);
    }
}

public class ProcessExecutor {
    private ProcessBuilderFactory processBuilderFactory;
    private ProcessExecutor(ProcessBuilderFactory processBuilderFactory) {
        this.processBuilderFactory = processBuilderFactory;
    }

    public void execute(String command) {
        ProcessBuilder processBuilder = processBuilderFactory.createProcessBuilder(command);
        Process process = processBuilder.start();

        int exitValue = process.waitFor();
        if (exitValue != 0) {
            throw new RuntimeException("a message here...");
        }
    }
}

and then you could make a unit test by injecting a mock `ProcessBuilderFactory`. You start writing the test, you create a mock `ProcessBuilderFactory`, returning a mock `ProcessBuilder`... damned, `ProcessBuilder` is `final` too :(

A strong reminder : write the test first !

So we have two options :

- introduce a new interface for wrapping the `ProcessBuilder` with a default implementation... in the same way we create the `ProcessBuilderFactory`

- undo the refactoring and look at PowerMock, for final class mocking

Problem

Original source