====== New Feed Checker ======
In this homework, we will develop a small software that checks if the feeds that we subscribed have any updates.

===== Basic components =====
Our main object, a **''FeedChecker''**, uses two other objects: a ''FeedReader'' and a ''FeedDatabase''.

  * A ''FeedReader'' provides the following methods:
    * ''fetch()'' reads the content of the feed.
    * ''getEntries()'' returns the list of entries in the feed.
    * ''getTitles()'' returns the list of titles of all entries.

  * A ''FeedDatabase'' provides the following methods:
    * ''getTitles()'' returns the list of titles of all entries.

The following interfaces describe both classes.

<code java>
import java.util.List;

public interface FeedReader {
	List<String> getTitles();
	void fetch();
}
</code>

<code java>
import java.util.List;

public interface FeedDatabase {
	List<String> getTitles();
}
</code>

Following is the skeleton of the Class Under Test, ''FeedChecker''.

<code java>
import java.util.List;

public class FeedChecker {

	public FeedChecker(FeedReader reader, FeedDatabase db) {}

	public void check() {}

	public List<String> getNewTitles() {}
}
</code>

When method ''check()'' is called, a ''FeedChecker'' would invoke ''fetch'' from the ''FeedReader'', then compares the list of titles returned from ''FeedReader'' and the titles returned from ''FeedDatabase''.  Method ''getNewTitle()'' returns a list of new titles, i.e., those titles returned by ''FeedReader'' which are not returned by ''FeedDatabase''.

===== FeedCheckerTest =====

Your task is to develop a unit test ''FeedCheckerTest'' for ''FeedChecker''.  You should include at least 3 interesting test cases  (Recall the slides on 'what to test'?).  Also, you have to implement ''FeedChecker'' so that it passes all test cases.

**Don't implement ''FeedReader'' or ''FeedDatabase''.  You should mock them instead.**