diff --git a/src/LongestSubstringWithoutRepeatingCharacters3.java b/src/main/java/com/leetcode/medium/LongestSubstringWithoutRepeatingCharacters3.java
similarity index 53%
rename from src/LongestSubstringWithoutRepeatingCharacters3.java
rename to src/main/java/com/leetcode/medium/LongestSubstringWithoutRepeatingCharacters3.java
index f70d4f8..7ea4853 100644
--- a/src/LongestSubstringWithoutRepeatingCharacters3.java
+++ b/src/main/java/com/leetcode/medium/LongestSubstringWithoutRepeatingCharacters3.java
@@ -1,16 +1,19 @@
-// Sliding Window, Hash Table, String
+// Tags: Sliding Window, HashSet, String
+package com.leetcode.medium;
 
 import java.util.HashSet;
+import java.util.Set;
 
 public class LongestSubstringWithoutRepeatingCharacters3 {
-    /*
-        Time complexity : O(2n) = O(n). In the worst case each character will be visited twice by l and r.
-        Space complexity : O(n)
+    /**
+     * Time complexity : O(2n) = O(n). In the worst case each character will be visited twice by l and r.
+     * <p>
+     * Space complexity : O(n)
      */
     public int lengthOfLongestSubstring(String s) {
         int res = 0;
         int l = 0;
-        HashSet<Character> hashSet = new HashSet<>();
+        Set<Character> hashSet = new HashSet<>();
         for (int r = 0; r < s.length(); r++) {
             while (hashSet.contains(s.charAt(r))) {
                 hashSet.remove(s.charAt(l));
@@ -21,9 +24,4 @@ public int lengthOfLongestSubstring(String s) {
         }
         return res;
     }
-
-    public static void main(String[] args) {
-        String s = "abcabcbb";
-        System.out.println(new LongestSubstringWithoutRepeatingCharacters3().lengthOfLongestSubstring(s));
-    }
 }
diff --git a/src/test/java/com/leetcode/medium/LongestSubstringWithoutRepeatingCharacters3Test.java b/src/test/java/com/leetcode/medium/LongestSubstringWithoutRepeatingCharacters3Test.java
new file mode 100644
index 0000000..4748efa
--- /dev/null
+++ b/src/test/java/com/leetcode/medium/LongestSubstringWithoutRepeatingCharacters3Test.java
@@ -0,0 +1,68 @@
+package com.leetcode.medium;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.time.Duration;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTimeoutPreemptively;
+
+public class LongestSubstringWithoutRepeatingCharacters3Test {
+    private LongestSubstringWithoutRepeatingCharacters3 solution;
+
+    @BeforeEach
+    void setUp() {
+        solution = new LongestSubstringWithoutRepeatingCharacters3();
+    }
+
+    @Test
+    void testLengthOfLongestSubstring_Example1() {
+        String s = "abcabcbb";
+        int expected = 3;
+
+        int result = assertTimeoutPreemptively(Duration.ofMillis(100), () -> solution.lengthOfLongestSubstring(s));
+
+        assertEquals(expected, result);
+    }
+
+    @Test
+    void testLengthOfLongestSubstring_Example2() {
+        String s = "bbbbb";
+        int expected = 1;
+
+        int result = assertTimeoutPreemptively(Duration.ofMillis(100), () -> solution.lengthOfLongestSubstring(s));
+
+        assertEquals(expected, result);
+    }
+
+    @Test
+    void testLengthOfLongestSubstring_Example3() {
+        String s = "pwwkew";
+        int expected = 3;
+
+        int result = assertTimeoutPreemptively(Duration.ofMillis(100), () -> solution.lengthOfLongestSubstring(s));
+
+        assertEquals(expected, result);
+    }
+
+    @Test
+    void testLengthOfLongestSubstring_Example4() {
+        String s = "tmmzuxt";
+        int expected = 5;
+
+        int result = assertTimeoutPreemptively(Duration.ofMillis(100), () -> solution.lengthOfLongestSubstring(s));
+
+        assertEquals(expected, result);
+    }
+
+    @Test
+    void testLengthOfLongestSubstring_Example5() {
+        String s = "aab";
+        int expected = 2;
+
+        int result = assertTimeoutPreemptively(Duration.ofMillis(100), () -> solution.lengthOfLongestSubstring(s));
+
+        assertEquals(expected, result);
+    }
+}