Add Stack.

src/data-structures/stack/__test__/Stack.test.js

@@ -0,0 +1,51 @@
+import Stack from '../Stack';
+
+describe('Stack', () => {
+  it('should create empty stack', () => {
+    const stack = new Stack();
+    expect(stack).not.toBeNull();
+    expect(stack.linkedList).not.toBeNull();
+  });
+
+  it('should stack data to stack', () => {
+    const stack = new Stack();
+
+    stack.push(1);
+    stack.push(2);
+
+    expect(stack.linkedList.toString()).toBe('1,2');
+  });
+
+  it('should peek data from stack', () => {
+    const stack = new Stack();
+
+    expect(stack.peek()).toBeNull();
+
+    stack.push(1);
+    stack.push(2);
+
+    expect(stack.peek()).toBe(2);
+    expect(stack.peek()).toBe(2);
+  });
+
+  it('should check if stack is empty', () => {
+    const stack = new Stack();
+
+    expect(stack.isEmpty()).toBeTruthy();
+
+    stack.push(1);
+
+    expect(stack.isEmpty()).toBeFalsy();
+  });
+
+  it('should pop data from stack', () => {
+    const stack = new Stack();
+
+    stack.push(1);
+    stack.push(2);
+
+    expect(stack.pop()).toBe(2);
+    expect(stack.pop()).toBe(1);
+    expect(stack.isEmpty()).toBeTruthy();
+  });
+});