diff --git a/.idea/modules.xml b/.idea/modules.xml
new file mode 100644
index 0000000..57e052a
--- /dev/null
+++ b/.idea/modules.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/modules/module4/Pricenton1.module4.test.iml" filepath="$PROJECT_DIR$/.idea/modules/module4/Pricenton1.module4.test.iml" />
+    </modules>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/modules/module4/Pricenton1.module4.test.iml b/.idea/modules/module4/Pricenton1.module4.test.iml
new file mode 100644
index 0000000..2c66d96
--- /dev/null
+++ b/.idea/modules/module4/Pricenton1.module4.test.iml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module version="4">
+  <component name="AdditionalModuleElements">
+    <content url="file://$MODULE_DIR$/../../../module4/src/test" dumb="true">
+      <sourceFolder url="file://$MODULE_DIR$/../../../module4/src/test/java" isTestSource="true" />
+    </content>
+  </component>
+</module>
\ No newline at end of file
diff --git a/Roadmaps/datastructures.md b/Roadmaps/datastructures.md
index e0513b9..de7cc7f 100644
--- a/Roadmaps/datastructures.md
+++ b/Roadmaps/datastructures.md
@@ -1,10 +1,18 @@
-#Data Structures
+# Data Structures
 
-    1. Stacks:
-        - Linear data structure
-        - Can have various implementations
-        - Should support (LIFO)
-        - Primitive implementation (Using arrays of primitive data types)
-        - Other implementations (Using linked lists)
-    2. Queues:
-        
\ No newline at end of file
+1. Stacks:
+   - [API](../module4/src/main/java/com/hithomelabs/princeton1/module4/Stack.java)
+   - [Sample client](../clients/src/main/java/com/hithomelabs/clients/ArrayStackClient.java)
+   - Linear data structure
+   - Can have various implementations
+   - Should support (LIFO)
+   - [Primitive implementation](../module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayStack.java) (Using arrays of primitive data types)
+   - [Other implementations](../module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedStack.java) (Using linked lists)
+2. Queues:
+   - [API](../module4/src/main/java/com/hithomelabs/princeton1/module4/Queue.java)
+   - [sample Client](../clients/src/main/java/com/hithomelabs/clients/LinkedQueueClient.java)
+   - Linear data structure.
+   - Can have various implementations.
+   - Should support FIFO.
+   - [Primitive implementation](../module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayQueue.java) (Using array of primitive data types)
+   - Other implementation ([using linked lists](../module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedQueue.java))
\ No newline at end of file
diff --git a/module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayQueue.java b/module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayQueue.java
index 4e8988e..8576647 100644
--- a/module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayQueue.java
+++ b/module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayQueue.java
@@ -1,8 +1,9 @@
 package com.hithomelabs.princeton1.module4;
 
-import javax.annotation.Nonnull;
 import java.util.Iterator;
 
+import javax.annotation.Nonnull;
+
 public class ArrayQueue<E> extends Queue<E>{
 
     // insertion from tail, removal from head
diff --git a/module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayStack.java b/module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayStack.java
index 0ae2eb6..93b3f30 100644
--- a/module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayStack.java
+++ b/module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayStack.java
@@ -1,13 +1,13 @@
 package com.hithomelabs.princeton1.module4;
-import javax.annotation.Nonnull;
 import java.util.Iterator;
+import javax.annotation.Nonnull;
 
 // Concrete implementation of stack using arrays
 // Creating a generic stack of type E
 public class ArrayStack<E> extends Stack<E> {
 
     // Capacity and size are two variables, capacity determines total capacity of array, capacity defaults at 10
-    // Everytime size == capacity, capacity = 2 * capacity
+    // every time size == capacity, capacity = 2 * capacity
     private static final int DEFAULT_CAPACITY = 10;
     private int capacity;
     private int size;
@@ -18,7 +18,7 @@ public class ArrayStack<E> extends Stack<E> {
         arr = (E[]) new Object[this.capacity];
     }
 
-    // Constructor chaining, default constructor will call parametrised constructor with default initial capacity 10
+    // Constructor chaining, default constructor will call parametrized constructor with default initial capacity 10
     public ArrayStack(){
         this(DEFAULT_CAPACITY);
     }
@@ -64,7 +64,7 @@ public class ArrayStack<E> extends Stack<E> {
     }
 
     private void checkResize() {
-        if (size < capacity / 4 && capacity >= 40){
+        if (size < capacity / 4 && capacity >= 20){
             capacity = capacity / 2;
             changeCapacity(capacity);
         }
diff --git a/module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedQueue.java b/module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedQueue.java
index ec37bbe..b7e62ff 100644
--- a/module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedQueue.java
+++ b/module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedQueue.java
@@ -60,7 +60,7 @@ public class LinkedQueue<E> extends Queue<E>{
             Node current = head;
             @Override
             public boolean hasNext() {
-                return current != tail;
+                return current != null;
             }
 
             @Override
diff --git a/module4/src/test/java/com/hithomelabs/princeton1/module4/ArrayQueueTest.java b/module4/src/test/java/com/hithomelabs/princeton1/module4/ArrayQueueTest.java
new file mode 100644
index 0000000..67ccd0e
--- /dev/null
+++ b/module4/src/test/java/com/hithomelabs/princeton1/module4/ArrayQueueTest.java
@@ -0,0 +1,76 @@
+package com.hithomelabs.princeton1.module4;
+
+import java.util.Iterator;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ArrayQueueTest {
+
+    private Queue<Integer> queue;
+
+    @BeforeEach
+    void setUp() {
+        queue = new ArrayQueue<Integer>();
+    }
+
+    @AfterEach
+    void tearDown() {
+        queue = null;
+    }
+
+    @Test
+    @DisplayName("Empty queue must return size zero")
+    public void testEmptyQueueSize(){
+        assertEquals(0, queue.size());
+    }
+
+    @Test
+    @DisplayName("Enqueuing must work as expected")
+    public void testEnqueue(){
+        queue.enqueue(1);
+        queue.enqueue(2);
+        assertEquals(2,queue.size());
+        Iterator<Integer> iterator = queue.iterator();
+        assertEquals(1, iterator.next());
+        assertEquals(2, iterator.next());
+    }
+
+    @Test
+    @DisplayName("Dequeueing must work as expected")
+    public void testDequeue(){
+        queue.enqueue(1);
+        queue.enqueue(2);
+        assertEquals(1, queue.dequeue());
+        queue.enqueue(3);
+        assertEquals(2, queue.size());
+        assertEquals(2, queue.dequeue());
+        assertEquals(3, queue.dequeue());
+        assertEquals(0, queue.size());
+        assertNull(queue.dequeue());
+    }
+
+    @Test
+    @DisplayName("Testing resizable array and iterator")
+    public void testResize(){
+        for(int i = 0; i < 21; i++)
+            queue.enqueue(i);
+        for(int i = 0; i < 13; i++){
+            queue.dequeue();
+        }
+        assertEquals(13, queue.dequeue());
+        assertEquals(7,queue.size());
+        Integer[] arr = new Integer[queue.size()];
+        Iterator<Integer> iterator = queue.iterator();
+        int count = 0;
+        while(iterator.hasNext()){
+            arr[count++] = iterator.next();
+        }
+        assertArrayEquals(new Integer[]{14, 15, 16, 17, 18, 19, 20}, arr);
+    }
+
+}
\ No newline at end of file
diff --git a/module4/src/test/java/com/hithomelabs/princeton1/module4/ArrayStackTest.java b/module4/src/test/java/com/hithomelabs/princeton1/module4/ArrayStackTest.java
new file mode 100644
index 0000000..c9ab765
--- /dev/null
+++ b/module4/src/test/java/com/hithomelabs/princeton1/module4/ArrayStackTest.java
@@ -0,0 +1,85 @@
+package com.hithomelabs.princeton1.module4;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.util.Iterator;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ArrayStackTest {
+
+    private Stack<String> stack;
+
+    @BeforeEach
+    void setUp() {
+        stack = new ArrayStack<String>();
+    }
+
+    @AfterEach
+    void tearDown() {
+        stack = null;
+    }
+
+    @Test
+    @DisplayName("Empty stack must return size zero")
+    public void testEmptyStackSize(){
+        assertEquals(0, stack.size());
+    }
+
+    @Test
+    @DisplayName("Push must work as expected")
+    public void testEnqueue(){
+        stack.push("Hello");
+        stack.push("World");
+        assertEquals(2,stack.size());
+        Iterator<String> iterator = stack.iterator();
+        assertEquals("Hello", iterator.next());
+        assertEquals("World", iterator.next());
+    }
+
+    @Test
+    @DisplayName("Pop must work as expected")
+    public void testDequeue(){
+        stack.push("hello");
+        stack.push("world");
+        assertEquals("world", stack.pop());
+        stack.push("I");
+        assertEquals(2, stack.size());
+        assertEquals("I", stack.pop());
+        assertEquals("hello", stack.pop());
+        assertEquals(0, stack.size());
+        assertNull(stack.pop());
+    }
+
+    @Test
+    @DisplayName("Testing resizable array and iterator")
+    public void testResize(){
+        stack.push("Hello");
+        stack.push("world");
+        stack.push("I");
+        stack.push("am");
+        stack.push("testing");
+        stack.push("my");
+        stack.push("implementation");
+        stack.push("of");
+        stack.push("Stacks");
+        stack.push("Data");
+        stack.push("Structure");
+        assertEquals("Structure", stack.pop());
+        int counter = 6;
+        while(counter-- > 0)
+            stack.pop();
+        assertEquals(4,stack.size());
+        String[] arr = new String[stack.size()];
+        Iterator<String> iterator = stack.iterator();
+        int count = 0;
+        while(iterator.hasNext()){
+            arr[count++] = iterator.next();
+        }
+        assertArrayEquals(new String[]{"Hello", "world", "I", "am"}, arr);
+    }
+
+}
\ No newline at end of file
diff --git a/module4/src/test/java/com/hithomelabs/princeton1/module4/LinkedQueueTest.java b/module4/src/test/java/com/hithomelabs/princeton1/module4/LinkedQueueTest.java
new file mode 100644
index 0000000..915cf4a
--- /dev/null
+++ b/module4/src/test/java/com/hithomelabs/princeton1/module4/LinkedQueueTest.java
@@ -0,0 +1,76 @@
+package com.hithomelabs.princeton1.module4;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.util.Iterator;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class LinkedQueueTest {
+
+    private Queue<Integer> queue;
+
+    @BeforeEach
+    void setUp() {
+        queue = new LinkedQueue<>();
+    }
+
+    @AfterEach
+    void tearDown() {
+        queue = null;
+    }
+
+
+    @Test
+    @DisplayName("Empty queue must return size zero")
+    public void testEmptyQueueSize(){
+        assertEquals(0, queue.size());
+    }
+
+    @Test
+    @DisplayName("Enqueuing must work as expected")
+    public void testEnqueue(){
+        queue.enqueue(1);
+        queue.enqueue(2);
+        assertEquals(2,queue.size());
+        Iterator<Integer> iterator = queue.iterator();
+        assertEquals(1, iterator.next());
+        assertEquals(2, iterator.next());
+    }
+
+    @Test
+    @DisplayName("Dequeueing must work as expected")
+    public void testDequeue(){
+        queue.enqueue(1);
+        queue.enqueue(2);
+        assertEquals(1, queue.dequeue());
+        queue.enqueue(3);
+        assertEquals(2, queue.size());
+        assertEquals(2, queue.dequeue());
+        assertEquals(3, queue.dequeue());
+        assertEquals(0, queue.size());
+        assertNull(queue.dequeue());
+    }
+
+    @Test
+    @DisplayName("Testing resizable array and iterator")
+    public void testResize(){
+        for(int i = 0; i < 21; i++)
+            queue.enqueue(i);
+        for(int i = 0; i < 13; i++){
+            queue.dequeue();
+        }
+        assertEquals(13, queue.dequeue());
+        assertEquals(7,queue.size());
+        Integer[] arr = new Integer[queue.size()];
+        Iterator<Integer> iterator = queue.iterator();
+        int count = 0;
+        while(iterator.hasNext()){
+            arr[count++] = iterator.next();
+        }
+        assertArrayEquals(new Integer[]{14, 15, 16, 17, 18, 19, 20}, arr);
+    }
+}
\ No newline at end of file