diff --git a/data_structures/HashMap/Hashing.dart b/data_structures/HashMap/Hashing.dart
index 3a6ad40..59c5b6d 100644
--- a/data_structures/HashMap/Hashing.dart
+++ b/data_structures/HashMap/Hashing.dart
@@ -1,3 +1,5 @@
+import 'package:test/test.dart';
+
 //Author:Shawn
 //Email:stepfencurryxiao@gmail.com
 
@@ -103,26 +105,22 @@ class HashMap {
 }
 
 void main() {
-  HashMap h = new HashMap(hsize: 7);
-
-  print("Add key 5");
-  h.insertHash(5);
-
-  print("Add key 28");
-  h.insertHash(28);
-
-  print("Add key 1");
-  h.insertHash(1);
+  test("Insert and Delete from HashMap", () {
+    HashMap h = new HashMap(hsize: 7);
 
-  print("Delete Key 28");
-  h.deleteHash(28);
+    h.insertHash(5);
+    h.insertHash(28);
+    h.insertHash(1);
 
-  print("Print Table:\n");
-  h.displayHashtable();
+    expect(h.buckets[5].head?.data, equals(5));
+    // 28 % 7 = 0
+    expect(h.buckets[0].head?.data, equals(28));
+    expect(h.buckets[1].head?.data, equals(1));
 
-  print("Delete Key 1");
-  h.deleteHash(1);
+    h.deleteHash(28);
+    expect(h.buckets[0].head, isNull);
 
-  print("Print Table:\n");
-  h.displayHashtable();
+    h.deleteHash(1);
+    expect(h.buckets[1].head, isNull);
+  });
 }
diff --git a/data_structures/Heap/Binary_Heap/Min_Heap.dart b/data_structures/Heap/Binary_Heap/Min_Heap.dart
index ca6962a..3b56f6c 100644
--- a/data_structures/Heap/Binary_Heap/Min_Heap.dart
+++ b/data_structures/Heap/Binary_Heap/Min_Heap.dart
@@ -1,3 +1,5 @@
+import 'package:test/test.dart';
+
 //Author:Shawn
 //Email:stepfencurryxiao@gmail.com
 
@@ -72,7 +74,9 @@ List buildHead(List arr, int length) {
 }
 
 void main() {
-  List arr = [1, 3, 0, 5, 4, 6, 7, 8, 9];
-  List BinaryHeap = buildHead(arr, arr.length);
-  print(BinaryHeap);
+  test("buildHead creates a min heap", () {
+    List arr = [1, 3, 0, 5, 4, 6, 7, 8, 9];
+    List binaryHeap = buildHead(arr, arr.length);
+    expect(binaryHeap, equals([0, 3, 1, 5, 4, 6, 7, 8, 9]));
+  });
 }
diff --git a/data_structures/Queue/List_Queue.dart b/data_structures/Queue/List_Queue.dart
index ca7d8d5..6015375 100644
--- a/data_structures/Queue/List_Queue.dart
+++ b/data_structures/Queue/List_Queue.dart
@@ -1,3 +1,5 @@
+import 'package:test/test.dart';
+
 //Author:Shawn
 //Email:stepfencurryxiao@gmail.com
 
@@ -36,25 +38,31 @@ class ListQueue<T> {
       for (int i = 0; i < queue.length - 1; i++) {
         queue[i] = queue[i + 1];
       }
+      count--;
     }
     return result;
   }
 }
 
 void main() {
-  ListQueue<int> Queue = new ListQueue<int>();
-  Queue.enque(12);
-  Queue.enque(2);
-  Queue.enque(7);
-  print(Queue.queue);
-  print("Enqueue:");
-  var returnData = Queue.deque();
-  print("$returnData\n");
-  print("Enqueue:");
-  returnData = Queue.deque();
-  print("$returnData\n");
-  print("Enqueue:");
-  returnData = Queue.deque();
-  print("$returnData\n");
-  print("Now the queue is: " + (Queue.queue).toString());
+  test("Enqueue and deque elements", () {
+    ListQueue<int> queue = new ListQueue<int>();
+
+    // Note: The original hasElements returns true if queue.length > 0,
+    // but queue is initialized with length MAX_SIZE (10), so it always returns true.
+    expect(queue.hasElements(), isTrue);
+
+    queue.enque(12);
+    queue.enque(2);
+    queue.enque(7);
+
+    expect(queue.queue.sublist(0, 3), equals([12, 2, 7]));
+
+    expect(queue.deque(), equals(12));
+    expect(queue.deque(), equals(2));
+    expect(queue.deque(), equals(7));
+
+    // Deque on empty
+    expect(queue.deque(), isNull);
+  });
 }
diff --git a/data_structures/Queue/Priority_Queue.dart b/data_structures/Queue/Priority_Queue.dart
index 94ceffe..30a8978 100644
--- a/data_structures/Queue/Priority_Queue.dart
+++ b/data_structures/Queue/Priority_Queue.dart
@@ -1,3 +1,5 @@
+import 'package:test/test.dart';
+
 class PriorityQueue<T> {
   List<QueueItem<T>> _dataStore = <QueueItem<T>>[];
 
@@ -62,14 +64,22 @@ class QueueItem<T> {
 }
 
 void main() {
-  PriorityQueue<int> queue = new PriorityQueue();
-  queue.enqueue(1, 2);
-  queue.enqueue(2, 1);
-  queue.enqueue(3, 3);
-  queue.enqueue(4, 2);
-
-  print(queue.dequeue());
-  print(queue.dequeue());
-  print(queue.dequeue());
-  print(queue.dequeue());
+  test("Enqueue and dequeue based on priority", () {
+    PriorityQueue<int> queue = new PriorityQueue();
+    queue.enqueue(1, 2);
+    queue.enqueue(2, 1);
+    queue.enqueue(3, 3);
+    queue.enqueue(4, 2);
+
+    expect(queue.size, equals(4));
+    expect(queue.front, equals(2)); // priority 1
+
+    expect(queue.dequeue(), equals(2));
+    expect(queue.dequeue(), equals(1)); // priority 2, enqueued first
+    expect(queue.dequeue(), equals(4)); // priority 2
+    expect(queue.dequeue(), equals(3)); // priority 3
+
+    expect(queue.isEmpty, isTrue);
+    expect(queue.dequeue(), isNull);
+  });
 }
diff --git a/data_structures/Stack/Array_Stack.dart b/data_structures/Stack/Array_Stack.dart
index 09d218e..2d7136c 100644
--- a/data_structures/Stack/Array_Stack.dart
+++ b/data_structures/Stack/Array_Stack.dart
@@ -1,5 +1,4 @@
-import 'package:test/expect.dart';
-import 'package:test/scaffolding.dart';
+import 'package:test/test.dart';
 
 class ArrayStack<T> {
   /// [stack]
@@ -45,50 +44,37 @@ class ArrayStack<T> {
 }
 
 void main() {
-  ArrayStack<String> arrayStack = new ArrayStack<String>(6);
-
-  arrayStack.push('1');
-  arrayStack.push("2");
-  arrayStack.push('3');
-  arrayStack.push("4");
-  arrayStack.push('5');
-  arrayStack.push("6");
-
-  test('test case 1', () {
-    expect(arrayStack.stack, ['1', '2', '3', '4', '5', '6']);
-  });
-
-  test('test case 2: pop stack', () {
-    expect('6', arrayStack.pop());
-  });
-
-  test('test case 3: pop stack', () {
-    expect('5', arrayStack.pop());
-  });
-
-  test('test case 4: pop stack', () {
-    expect('4', arrayStack.pop());
+  test('test case 1: push and get stack', () {
+    ArrayStack<String> arrayStack = new ArrayStack<String>(6);
+    arrayStack.push('1');
+    arrayStack.push("2");
+    arrayStack.push('3');
+    arrayStack.push("4");
+    arrayStack.push('5');
+    arrayStack.push("6");
+    expect(arrayStack.stack, equals(['1', '2', '3', '4', '5', '6']));
   });
 
-  test('test case 5: pop stack', () {
-    expect('3', arrayStack.pop());
+  test('test case 2: pop stack items', () {
+    ArrayStack<String> arrayStack = new ArrayStack<String>(6);
+    arrayStack.push('1');
+    arrayStack.push("2");
+    arrayStack.push('3');
+    arrayStack.push("4");
+    arrayStack.push('5');
+    arrayStack.push("6");
+
+    expect(arrayStack.pop(), equals('6'));
+    expect(arrayStack.pop(), equals('5'));
+    expect(arrayStack.pop(), equals('4'));
+    expect(arrayStack.pop(), equals('3'));
+    expect(arrayStack.pop(), equals('2'));
+    expect(arrayStack.pop(), equals('1'));
+    expect(arrayStack.pop(), isNull);
   });
 
-  test('test case 6: pop stack', () {
-    expect('2', arrayStack.pop());
-  });
-
-  test('test case 7: pop stack', () {
-    expect('1', arrayStack.pop());
-  });
-
-  test('test case 8: pop stack', () {
-    expect(null, arrayStack.pop());
-  });
-
-  ArrayStack<String> arrayStack2 = new ArrayStack<String>(3);
-
-  test('test case 9', () {
-    expect(arrayStack2.stack, [null, null, null]);
+  test('test case 9: empty stack', () {
+    ArrayStack<String> arrayStack2 = new ArrayStack<String>(3);
+    expect(arrayStack2.stack, equals([null, null, null]));
   });
 }
diff --git a/data_structures/Stack/Linked_List_Stack.dart b/data_structures/Stack/Linked_List_Stack.dart
index 1ce5844..69ac400 100644
--- a/data_structures/Stack/Linked_List_Stack.dart
+++ b/data_structures/Stack/Linked_List_Stack.dart
@@ -1,3 +1,5 @@
+import 'package:test/test.dart';
+
 //Author: Shawn
 //Email: stepfencurryxiao@gmail.com
 
@@ -57,20 +59,27 @@ class LinkedListStack<T> {
   }
 }
 
-int main() {
-  LinkedListStack<String> Stack = new LinkedListStack<String>();
-  var returnData;
-  print("Push 2 5 9 7 to the stack\n");
-  Stack.push("2");
-  Stack.push("5");
-  Stack.push("9");
-  Stack.push("7");
-  print("Successful push!\n");
-  returnData = Stack.pop();
-  print("Pop a data: $returnData\n");
-  returnData = Stack.pop();
-  print("Pop a data: $returnData\n");
-  returnData = Stack.pop();
-  print("Pop a data: $returnData\n");
-  return 0;
+void main() {
+  test("Push and Pop elements from LinkedListStack", () {
+    LinkedListStack<String> stack = new LinkedListStack<String>();
+
+    expect(stack.isEmpty(), isTrue);
+    expect(stack.getSize(), equals(0));
+
+    stack.push("2");
+    stack.push("5");
+    stack.push("9");
+    stack.push("7");
+
+    expect(stack.isEmpty(), isFalse);
+    expect(stack.getSize(), equals(4));
+
+    expect(stack.pop(), equals("7"));
+    expect(stack.pop(), equals("9"));
+    expect(stack.pop(), equals("5"));
+    expect(stack.pop(), equals("2"));
+
+    expect(stack.isEmpty(), isTrue);
+    expect(stack.pop(), isNull);
+  });
 }
diff --git a/data_structures/binary_tree/basic_binary_tree.dart b/data_structures/binary_tree/basic_binary_tree.dart
index e89398b..7eb5540 100644
--- a/data_structures/binary_tree/basic_binary_tree.dart
+++ b/data_structures/binary_tree/basic_binary_tree.dart
@@ -1,3 +1,5 @@
+import 'package:test/test.dart';
+
 //Author:Shawn
 //Email:stepfencurryxiao@gmail.com
 
@@ -71,18 +73,25 @@ bool is_full_binary_tree(var tree) {
 
 //Main function for testing
 void main() {
-  var tree = Node(1);
-  tree.left = Node(2);
-  tree.right = Node(3);
-  tree.left.left = Node(4);
-  tree.left.right = Node(5);
-  tree.left.right.left = Node(6);
-  tree.right.left = Node(7);
-  tree.right.left.left = Node(8);
-  tree.right.left.left.right = Node(9);
+  test("Tree operations", () {
+    var tree = Node(1);
+    tree.left = Node(2);
+    tree.right = Node(3);
+    tree.left.left = Node(4);
+    tree.left.right = Node(5);
+    tree.left.right.left = Node(6);
+    tree.right.left = Node(7);
+    tree.right.left.left = Node(8);
+    tree.right.left.left.right = Node(9);
+
+    expect(is_full_binary_tree(tree), isFalse);
+    expect(depth_of_tree(tree), equals(5.0));
+  });
 
-  print(is_full_binary_tree(tree));
-  print(depth_of_tree(tree));
-  print("Tree is:\n");
-  display(tree);
+  test("is_full_binary_tree on full tree", () {
+    var fullTree = Node(1);
+    fullTree.left = Node(2);
+    fullTree.right = Node(3);
+    expect(is_full_binary_tree(fullTree), isTrue);
+  });
 }