diff --git a/.gitignore b/.gitignore
index eb79dd5f..c7f4bdc0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 node_modules
 .idea
+coverage
diff --git a/jest.config.js b/jest.config.js
new file mode 100644
index 00000000..0f6d7fa8
--- /dev/null
+++ b/jest.config.js
@@ -0,0 +1,5 @@
+module.exports = {
+  verbose: false,
+  collectCoverage: true,
+  coverageDirectory: './coverage/',
+};
diff --git a/src/data-structures/priority-queue/__test__/PriorityQueue.test.js b/src/data-structures/priority-queue/__test__/PriorityQueue.test.js
index b628553f..1473d2d8 100644
--- a/src/data-structures/priority-queue/__test__/PriorityQueue.test.js
+++ b/src/data-structures/priority-queue/__test__/PriorityQueue.test.js
@@ -26,8 +26,10 @@ describe('PriorityQueue', () => {
     priorityQueue.add(10, 1);
     priorityQueue.add(5, 2);
     priorityQueue.add(100, 0);
+    priorityQueue.add(200, 0);
 
     expect(priorityQueue.poll()).toBe(100);
+    expect(priorityQueue.poll()).toBe(200);
     expect(priorityQueue.poll()).toBe(10);
     expect(priorityQueue.poll()).toBe(5);
   });
diff --git a/src/data-structures/queue/__test__/Queue.test.js b/src/data-structures/queue/__test__/Queue.test.js
index d55292d9..587e37b5 100644
--- a/src/data-structures/queue/__test__/Queue.test.js
+++ b/src/data-structures/queue/__test__/Queue.test.js
@@ -46,6 +46,7 @@ describe('Queue', () => {
 
     expect(queue.dequeue()).toBe(1);
     expect(queue.dequeue()).toBe(2);
+    expect(queue.dequeue()).toBeNull();
     expect(queue.isEmpty()).toBeTruthy();
   });
 });
diff --git a/src/data-structures/stack/__test__/Stack.test.js b/src/data-structures/stack/__test__/Stack.test.js
index cf8addcf..63978243 100644
--- a/src/data-structures/stack/__test__/Stack.test.js
+++ b/src/data-structures/stack/__test__/Stack.test.js
@@ -46,6 +46,7 @@ describe('Stack', () => {
 
     expect(stack.pop()).toBe(2);
     expect(stack.pop()).toBe(1);
+    expect(stack.pop()).toBeNull();
     expect(stack.isEmpty()).toBeTruthy();
   });
 });
diff --git a/src/data-structures/tree/__test__/BinaryTreeNode.test.js b/src/data-structures/tree/__test__/BinaryTreeNode.test.js
index 36c61415..54535e53 100644
--- a/src/data-structures/tree/__test__/BinaryTreeNode.test.js
+++ b/src/data-structures/tree/__test__/BinaryTreeNode.test.js
@@ -99,5 +99,7 @@ describe('BinaryTreeNode', () => {
 
     expect(rootNode.replaceChild(rootNode.right, replacementNode)).toBeTruthy();
     expect(rootNode.traverseInOrder()).toEqual([1, 2, 5]);
+
+    expect(rootNode.replaceChild(new BinaryTreeNode(), new BinaryTreeNode())).toBeFalsy();
   });
 });