This is a quick Fizz Buzz exercise I did to teach a high school student the concepts behind TDD. Method naming and code structure could be better, but I just needed to illustrate a point. I felt the exercise went well and I thought it might be worth while to keep the code.

FizzBuzzTest.java

package com.wanooknox.fizzbuzz;

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

import static org.junit.Assert.assertEquals;

public class FizzBuzzTest {

    private FizzBuzzEngine fizzBuzzEngine;

    @Before
    public void setup() {
        fizzBuzzEngine = new FizzBuzzEngine();
    }

    @Test
    public void isMultipleOf3_shouldReturnTrue_whenGivenExactly3() {
        // Setup
        boolean expected = true;
        int input = 3;

        // Execute
        boolean actual = fizzBuzzEngine.isMultipleOf3(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void isMultipleOf3_shouldReturnTrue_whenGiven6() {
        // Setup
        boolean expected = true;
        int input = 6;

        // Execute
        boolean actual = fizzBuzzEngine.isMultipleOf3(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void isMultipleOf3_shouldReturnFalse_whenGiven5() {
        // Setup
        boolean expected = false;
        int input = 5;

        // Execute
        boolean actual = fizzBuzzEngine.isMultipleOf3(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void isMultipleOf5_shouldReturnTrue_whenGivenExactly5() {
        // Setup
        boolean expected = true;
        int input = 5;

        // Execute
        boolean actual = fizzBuzzEngine.isMultipleOf5(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void isMultipleOf5_shouldReturnTrue_whenGiven10() {
        // Setup
        boolean expected = true;
        int input = 10;

        // Execute
        boolean actual = fizzBuzzEngine.isMultipleOf5(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void isMultipleOf5_shouldReturnFalse_whenGiven3() {
        // Setup
        boolean expected = false;
        int input = 3;

        // Execute
        boolean actual = fizzBuzzEngine.isMultipleOf5(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void isMultipleOf5_shouldReturnFalse_whenGiven9() {
        // Setup
        boolean expected = false;
        int input = 9;

        // Execute
        boolean actual = fizzBuzzEngine.isMultipleOf5(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void fizzOrBuzzOrNumber_shouldReturnFizz_whenMultipleOf3() {
        // Setup
        String expected = "Fizz";
        int input = 6;

        // Execute
        String actual = fizzBuzzEngine.fizzOrBuzzOrNumber(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void fizzOrBuzzOrNumber_shouldReturnBuzz_whenMultipleOf5() {
        // Setup
        String expected = "Buzz";
        int input = 10;

        // Execute
        String actual = fizzBuzzEngine.fizzOrBuzzOrNumber(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void fizzOrBuzzOrNumber_shouldReturnFizzBuzz_whenMultipleOf3And5() {
        // Setup
        String expected = "FizzBuzz";
        int input = 15;

        // Execute
        String actual = fizzBuzzEngine.fizzOrBuzzOrNumber(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void fizzOrBuzzOrNumber_shouldReturnTheNumber_whenNotMultipleOf3Or5() {
        // Setup
        String expected = "14";
        int input = 14;

        // Execute
        String actual = fizzBuzzEngine.fizzOrBuzzOrNumber(input);

        // Assert
        assertEquals(expected, actual);
    }

    @Test
    public void dummy() {
        fizzBuzzEngine.doFizzBuzz();
    }

    private class FizzBuzzEngine {

        public void doFizzBuzz() {
            for (int i = 0; i < 100; i++) {
                System.out.println(fizzOrBuzzOrNumber(i));
            }
        }

        public String fizzOrBuzzOrNumber(int input) {
            String result = "";

            if (isMultipleOf3(input)) {
                result += "Fizz";
            }

            if (isMultipleOf5(input)) {
                result += "Buzz";
            }

            if (result == "") {
                return String.valueOf(input);
            } else {
                return result;
            }
        }

        public boolean isMultipleOf3(int value) {
            int divisor = 3;
            return ((value % divisor) == 0);
        }

        public boolean isMultipleOf5(int value) {
            return ((value % 5) == 0);
        }

    }

}