Add tests for factorial example. (#112)

03_recursion/java/03_factorial/src/Factorial2.java

@@ -0,0 +1,21 @@
+public class Factorial2 {
+    public static void main(String[] args) {
+        Factorial2 factorial2 = new Factorial2();
+        System.out.println("The factorial of 5 is " + factorial2.getFactorial(5));
+    }
+
+    public int getFactorial(int number) {
+        if (isZeroOrOne(number)) {
+            return 1;
+        }
+
+        return number * getFactorial(number - 1);
+    }
+
+    public boolean isZeroOrOne(int number) {
+        if (number > 1) {
+            return false;
+        }
+        return true;
+    }
+}

03_recursion/java/03_factorial/src/Factorial2Test.java

@@ -0,0 +1,20 @@
+import org.junit.Assert;
+import org.junit.Test;
+
+public class Factorial2Test {
+    @Test
+    public void testIsZeroOrOne() {
+        Factorial2 factorial2 = new Factorial2();
+
+        Assert.assertEquals(true, factorial2.isZeroOrOne(0));
+        Assert.assertEquals(true, factorial2.isZeroOrOne(1));
+        Assert.assertEquals(false, factorial2.isZeroOrOne(5));
+    }
+
+    @Test
+    public void testFactorial() {
+        Factorial2 factorial2 = new Factorial2();
+
+        Assert.assertEquals(120, factorial2.getFactorial(5));
+    }
+}