diff --git a/src/06-linked-list/__test__/circular-linked-list.test.ts b/src/06-linked-list/__test__/circular-linked-list.test.ts
new file mode 100644
index 00000000..2d61d380
--- /dev/null
+++ b/src/06-linked-list/__test__/circular-linked-list.test.ts
@@ -0,0 +1,133 @@
+import {describe, expect, test, beforeEach} from '@jest/globals';
+import CircularLinkedList from '../circular-linked-list';
+
+describe('CircularLinkedList', () => {
+  let circularList: CircularLinkedList<number>;
+
+  beforeEach(() => {
+    circularList = new CircularLinkedList<number>();
+  });
+
+  test('should create an empty list', () => {
+    expect(circularList.isEmpty()).toBe(true);
+    expect(circularList.getSize()).toBe(0);
+    expect(circularList.toString()).toBe('');
+  });
+
+  test('should append a single element', () => {
+    circularList.append(1);
+    expect(circularList.toString()).toBe('1');
+    expect(circularList.getSize()).toBe(1);
+  });
+
+  test('should append multiple elements', () => {
+    circularList.append(1);
+    circularList.append(2);
+    circularList.append(3);
+    expect(circularList.toString()).toBe('1 -> 2 -> 3');
+  });
+
+  test('should prepend an element', () => {
+    circularList.append(2);
+    circularList.append(3);
+    circularList.prepend(1);
+    expect(circularList.toString()).toBe('1 -> 2 -> 3');
+    expect(circularList.getSize()).toBe(3);
+  });
+
+  test('should insert at position 0 (delegates to prepend)', () => {
+    circularList.append(2);
+    circularList.append(3);
+    circularList.insert(0, 1);
+    expect(circularList.toString()).toBe('1 -> 2 -> 3');
+  });
+
+  test('should insert at a middle position', () => {
+    circularList.append(1);
+    circularList.append(3);
+    circularList.insert(1, 2);
+    expect(circularList.toString()).toBe('1 -> 2 -> 3');
+  });
+
+  test('should return false for insert at invalid position', () => {
+    circularList.append(1);
+    expect(circularList.insert(5, 99)).toBe(false);
+    expect(circularList.getSize()).toBe(1);
+  });
+
+  test('should removeAt head (position 0)', () => {
+    circularList.append(1);
+    circularList.append(2);
+    circularList.append(3);
+    circularList.removeAt(0);
+    expect(circularList.toString()).toBe('2 -> 3');
+    expect(circularList.getSize()).toBe(2);
+  });
+
+  test('should removeAt a middle position', () => {
+    circularList.append(1);
+    circularList.append(2);
+    circularList.append(3);
+    circularList.removeAt(1);
+    expect(circularList.toString()).toBe('1 -> 3');
+  });
+
+  test('should throw for removeAt invalid position', () => {
+    circularList.append(1);
+    expect(() => circularList.removeAt(5)).toThrow('Invalid position');
+  });
+
+  test('should remove an element by value', () => {
+    circularList.append(1);
+    circularList.append(2);
+    circularList.append(3);
+    circularList.remove(2);
+    expect(circularList.toString()).toBe('1 -> 3');
+  });
+
+  test('should return null when removing a non-existing element', () => {
+    circularList.append(1);
+    expect(circularList.remove(99)).toBeNull();
+  });
+
+  test('should find indexOf an existing element', () => {
+    circularList.append(10);
+    circularList.append(20);
+    circularList.append(30);
+    expect(circularList.indexOf(10)).toBe(0);
+    expect(circularList.indexOf(20)).toBe(1);
+    expect(circularList.indexOf(30)).toBe(2);
+  });
+
+  test('should return -1 for indexOf a non-existing element', () => {
+    circularList.append(1);
+    expect(circularList.indexOf(99)).toBe(-1);
+  });
+
+  test('should clear the list', () => {
+    circularList.append(1);
+    circularList.append(2);
+    circularList.clear();
+    expect(circularList.isEmpty()).toBe(true);
+    expect(circularList.toString()).toBe('');
+  });
+
+  test('should maintain circular structure after append', () => {
+    circularList.append(1);
+    circularList.append(2);
+    circularList.append(3);
+    const head = circularList.getHead();
+    expect(head?.next?.next?.next).toBe(head);
+  });
+
+  test('should reverse the list', () => {
+    circularList.append(1);
+    circularList.append(2);
+    circularList.append(3);
+    circularList.reverse();
+    const head = circularList.getHead();
+    expect(head?.element).toBe(3);
+    expect(head?.next?.element).toBe(2);
+    expect(head?.next?.next?.element).toBe(1);
+  });
+});
diff --git a/src/08-dictionary-hash/__test__/hash-table.test.ts b/src/08-dictionary-hash/__test__/hash-table.test.ts
new file mode 100644
index 00000000..59e26ebe
--- /dev/null
+++ b/src/08-dictionary-hash/__test__/hash-table.test.ts
@@ -0,0 +1,54 @@
+import {describe, expect, test, beforeEach} from '@jest/globals';
+import HashTable from '../hash-table';
+
+describe('HashTable', () => {
+  let hashTable: HashTable<string>;
+
+  beforeEach(() => {
+    hashTable = new HashTable<string>();
+  });
+
+  test('should put and get a value', () => {
+    hashTable.put('name', 'Alice');
+    expect(hashTable.get('name')).toBe('Alice');
+  });
+
+  test('should return undefined for a non-existent key', () => {
+    expect(hashTable.get('missing')).toBeUndefined();
+  });
+
+  test('should overwrite an existing key with put', () => {
+    hashTable.put('name', 'Alice');
+    hashTable.put('name', 'Bob');
+    expect(hashTable.get('name')).toBe('Bob');
+  });
+
+  test('should remove an existing key and return true', () => {
+    hashTable.put('name', 'Alice');
+    expect(hashTable.remove('name')).toBe(true);
+    expect(hashTable.get('name')).toBeUndefined();
+  });
+
+  test('should return false when removing a non-existent key', () => {
+    expect(hashTable.remove('missing')).toBe(false);
+  });
+
+  test('should store multiple keys', () => {
+    hashTable.put('name', 'Alice');
+    hashTable.put('city', 'London');
+    expect(hashTable.get('name')).toBe('Alice');
+    expect(hashTable.get('city')).toBe('London');
+  });
+
+  test('hash function returns consistent results', () => {
+    expect(hashTable.hash('name')).toBe(hashTable.hash('name'));
+    expect(hashTable.hash('abc')).toBeGreaterThanOrEqual(0);
+    expect(hashTable.hash('abc')).toBeLessThan(37);
+  });
+
+  test('should produce correct toString output', () => {
+    hashTable.put('name', 'Alice');
+    const result = hashTable.toString();
+    expect(result).toContain('Alice');
+  });
+});
diff --git a/src/08-dictionary-hash/hash-table.ts b/src/08-dictionary-hash/hash-table.ts
index d7e1c1da..df32bbfd 100644
--- a/src/08-dictionary-hash/hash-table.ts
+++ b/src/08-dictionary-hash/hash-table.ts
@@ -5,9 +5,6 @@ class HashTable<V> {
   private table: V[] = [];
 
   #loseLoseHashCode(key: string) {
-    // if (typeof key !== 'string') {
-    //   key = this.#elementToString(key);
-    // }
     const calcASCIIValue = (acc: number, char: string) => acc + char.charCodeAt(0);
     const hash = key.split('').reduce(calcASCIIValue, 0);
     return hash % 37;
@@ -19,21 +16,21 @@ class HashTable<V> {
 
   put(key: string, value: V) {
     const index = this.hash(key);
-    this.table[index] = value; 
+    this.table[index] = value;
     return true;
   }
 
-  get(key: string): V {
+  get(key: string): V | undefined {
     const index = this.hash(key);
     return this.table[index];
   }
 
-  remove(key: string) {
+  remove(key: string): boolean {
     if (key == null) {
       return false;
     }
     const index = this.hash(key);
-    if (this.table[index]) {
+    if (this.table[index] != null) {
       delete this.table[index];
       return true;
     }
@@ -44,7 +41,7 @@ class HashTable<V> {
     if (typeof data === 'object' && data !== null) {
       return JSON.stringify(data);
     } else {
-      return String(data); 
+      return String(data);
     }
   }
 
diff --git a/src/12-trie/__test__/trie.test.ts b/src/12-trie/__test__/trie.test.ts
new file mode 100644
index 00000000..13981929
--- /dev/null
+++ b/src/12-trie/__test__/trie.test.ts
@@ -0,0 +1,83 @@
+import {describe, expect, test, beforeEach} from '@jest/globals';
+import Trie from '../trie';
+
+describe('Trie', () => {
+  let trie: Trie;
+
+  beforeEach(() => {
+    trie = new Trie();
+  });
+
+  test('should return false for search on empty trie', () => {
+    expect(trie.search('hello')).toBe(false);
+  });
+
+  test('should insert and search a word', () => {
+    trie.insert('hello');
+    expect(trie.search('hello')).toBe(true);
+  });
+
+  test('should return false for a word that does not exist', () => {
+    trie.insert('hello');
+    expect(trie.search('world')).toBe(false);
+  });
+
+  test('should return false when searching a prefix that is not a full word', () => {
+    trie.insert('hello');
+    expect(trie.search('hell')).toBe(false);
+  });
+
+  test('should return true for startsWith with an existing prefix', () => {
+    trie.insert('hello');
+    expect(trie.startsWith('hel')).toBe(true);
+  });
+
+  test('should return false for startsWith with a non-existing prefix', () => {
+    trie.insert('hello');
+    expect(trie.startsWith('xyz')).toBe(false);
+  });
+
+  test('should return true for startsWith when the full word is the prefix', () => {
+    trie.insert('hello');
+    expect(trie.startsWith('hello')).toBe(true);
+  });
+
+  test('should insert multiple words with shared prefix', () => {
+    trie.insert('car');
+    trie.insert('card');
+    trie.insert('care');
+    expect(trie.search('car')).toBe(true);
+    expect(trie.search('card')).toBe(true);
+    expect(trie.search('care')).toBe(true);
+    expect(trie.startsWith('car')).toBe(true);
+    expect(trie.search('ca')).toBe(false);
+  });
+
+  test('should remove an existing word so search returns false', () => {
+    trie.insert('hello');
+    trie.remove('hello');
+    expect(trie.search('hello')).toBe(false);
+  });
+
+  test('should remove a word that is a prefix of another without affecting the longer word', () => {
+    trie.insert('car');
+    trie.insert('card');
+    trie.remove('car');
+    expect(trie.search('car')).toBe(false);
+    expect(trie.search('card')).toBe(true);
+  });
+
+  test('should return false when removing a non-existent word', () => {
+    trie.insert('hello');
+    expect(trie.remove('world')).toBe(false);
+  });
+
+  test('should keep startsWith working after removing a word that shares a prefix', () => {
+    trie.insert('car');
+    trie.insert('card');
+    trie.remove('card');
+    expect(trie.search('card')).toBe(false);
+    expect(trie.search('car')).toBe(true);
+    expect(trie.startsWith('car')).toBe(true);
+  });
+});
diff --git a/src/12-trie/trie.js b/src/12-trie/trie.js
index d61298a2..44a6eae0 100644
--- a/src/12-trie/trie.js
+++ b/src/12-trie/trie.js
@@ -60,7 +60,7 @@ class Trie {
     const shouldDeleteCurrentNode = this.#removeWord(node.children.get(char), word, index + 1);
     if (shouldDeleteCurrentNode) {
       node.children.delete(char);
-      return node.children.size === 0;
+      return node.children.size === 0 && !node.isEndOfWord;
     }
 
     return false;
diff --git a/src/12-trie/trie.ts b/src/12-trie/trie.ts
index 080921b8..7cc81789 100644
--- a/src/12-trie/trie.ts
+++ b/src/12-trie/trie.ts
@@ -67,7 +67,7 @@ class Trie {
     const shouldDeleteCurrentNode = this.#removeWord(node.children.get(char)!, word, index + 1);
     if (shouldDeleteCurrentNode) {
       node.children.delete(char);
-      return node.children.size === 0;
+      return node.children.size === 0 && !node.isEndOfWord;
     }
 
     return false;