Question

I’d like to have a helper class for getting the current date. I want to avoid having new Date() in code because of future testing issues (may need to return different time than system time) and I cannot use JodaTime to prevent the problem with testing.

I was thinking of a helper like this:

public interface DateHelper {

    /**
     * Returns the current date.
     */
    Date now();

}

But how can I supply mocks of this interface to the clients?
The only solution I can think of is this:

public ClientOfDateHelper {

    private DateHelper dateHelper;

    // no-arg constructor that instantiates a standard implementation of DateHelper
    public ClientOfDateHelper() {
        this.dateHelper = new DefaultDateHelper(); 
    }

    // constructor that can be used to pass mock to the client
    public ClientOfDateHelper(DateHelper suppliedDateHelper) {
        this.dateHelper = suppliedDateHelper;
    }

    public void foo() {
        Date today = dateHelper.now();
        // do some work that requires today's date
    }

}

Is there a more elegant solution that requires less code to use the DateHelper, yet it allows using mocks?

Answer 1

Ease of testing is one of the benefits of dependency injection. Using a framework like Spring allows you to externally configure your dependencies. So your implementation will run with your spring configuration, and your unit tests will run with the mocks you supply through constructor or property setters. This eliminates the need for the two constuctors above, you would just use one that accepts DateHelper.