FizzBuzzTest.java:

import static org.junit.Assert.*;

import org.junit.Before;
import org.junit.Test;



public class FizzBuzzTest {

    private static final Object[] ARRAY_OF_2_FIZZ = {2, "Fizz"};
    private static final Object[] ARRAY_OF_1_2 = {1, 2};
    private static final Object[] ARRAY_OF_FIZZ_7_8_FIZZ = {"Fizz", 7,
                                                            8, "Fizz"};
    private static final Object[] ARRAY_OF_BUZZ = {"Buzz"};
    private static final Object[] ARRAY_OF_FIZZBUZZ = {"FizzBuzz"};
    private static final Object[] ARRAY_OF_FIZZBUZZ_TO_FIZZ = { "FizzBuzz", 16,
                                                                17, "Fizz", 19,
                                                                "Buzz", "Fizz",
                                                                22, 23, "Fizz",
                                                                "Buzz", 26,
                                                                "Fizz", 28, 29,
                                                                "FizzBuzz"};

    FizzBuzz fizzBuzz = new FizzBuzz();

    @Before
    public void addFilters() {
        fizzBuzz.addFilter(new FizzBuzzFilter() {
            public String filter(int integer) {
                return integer % 3 == 0? "Fizz" : "";
            }
        });
        fizzBuzz.addFilter(new FizzBuzzFilter() {
            public String filter(int integer) {
                return integer % 5 == 0? "Buzz" : "";
            }
        });
    }
    
    @Test
    public void shouldReturn1And2AsIs() throws Exception {
        assertArrayEquals(ARRAY_OF_1_2, fizzBuzz.filter(range(1, 2)));
    }
    

    @Test
    public void shouldConvertThreeToFizz() throws Exception {
        assertArrayEquals(ARRAY_OF_2_FIZZ, fizzBuzz.filter(range(2, 3)));
    }

    @Test
    public void shouldConvert6And9ToFizz() throws Exception {
        assertArrayEquals(ARRAY_OF_FIZZ_7_8_FIZZ, fizzBuzz.filter(range(6, 9)));
    }
    
    @Test
    public void shouldConvert5ToBuzz() throws Exception {
        assertArrayEquals(ARRAY_OF_BUZZ, fizzBuzz.filter(range(5, 5)));
    }
    
    @Test
    public void shouldConvert15ToFizzBuzz() throws Exception {
        assertArrayEquals(ARRAY_OF_FIZZBUZZ, fizzBuzz.filter(range(15, 15)));
    }
    
    @Test
    public void shouldConvert15To30Correctly() throws Exception {
        assertArrayEquals(ARRAY_OF_FIZZBUZZ_TO_FIZZ,
                          fizzBuzz.filter(range(15, 30)));
    }

    private int[] range(int start, int end) {
        int[] range = new int[end-start+1];
        for (int count = 0; count < range.length; count++)
            range[count] = start+count;
        return range;
    }
}
FizzBuzz.java:

import java.util.ArrayList;


public class FizzBuzz {

    private ArrayList<FizzBuzzFilter> filters = new ArrayList<FizzBuzzFilter>();

    public Object[] filter(int[] integers) {
        Object[] result = new Object[integers.length];
        for (int i = 0; i < integers.length; i++) {
            result[i] = convert(integers[i]);
        }
        return result;
    }

    private Object convert(int integer) {
        String converted = applyFilters(integer);
        return "".equals(converted) ? integer : converted;
    }

    private String applyFilters(int integer) {
        String converted = "";
        for (FizzBuzzFilter filter : filters) {
            converted += filter.filter(integer);
        }
        return converted;
    }

    public void addFilter(FizzBuzzFilter fizzBuzzFilter) {
        filters.add(fizzBuzzFilter);
    }
}