All test written and passed.

src/main/java/FizzBuzz.java

@@ -1,2 +1,15 @@
 public class FizzBuzz {
+    public static String of(int number) {
+
+        if ((number % 3 == 0) && (number % 5 == 0)) {
+            return "FizzBuzz";
+        } else if (number % 3 == 0) {
+            return "Fizz";
+        } else if (number % 5 == 0) {
+            return "Buzz";
+        } else {
+            return Integer.toString(number);
+        }
+
+    }
 }

src/test/java/FizzBuzzTest.java

@@ -1,2 +1,59 @@
+import org.junit.Assert;
+import org.junit.Test;
+
 public class FizzBuzzTest {
+
+    @Test
+    public void fizzTest() {
+        //Given
+        int number = 12;
+        String expectedOutput = "Fizz";
+
+        //When
+        String actualOutput = FizzBuzz.of(number);
+
+        //Then
+        Assert.assertEquals(expectedOutput, actualOutput);
+    }
+
+    @Test
+    public void buzzTest() {
+        //Given
+        int number = 20;
+        String expectedOutput = "Buzz";
+
+        //When
+        String actualOutput = FizzBuzz.of(number);
+
+        //Then
+        Assert.assertEquals(expectedOutput, actualOutput);
+    }
+
+    @Test
+    public void fizzbuzzTest() {
+        //Given
+        int number = 15;
+        String expectedOutput = "FizzBuzz";
+
+        //When
+        String actualOutput = FizzBuzz.of(number);
+
+        //Then
+        Assert.assertEquals(expectedOutput, actualOutput);
+    }
+
+    @Test
+    public void elseTest() {
+        //Given
+        int number = 22;
+        String expectedOutput = "22";
+
+        //When
+        String actualOutput = FizzBuzz.of(number);
+
+        //Then
+        Assert.assertEquals(expectedOutput, actualOutput);
+    }
+
+
 }