tests: added stack unit tests (#398)

Signed-off-by: Anthony D. Mays <anthony@morganlatimer.com>

Author: anthonydmays

lesson_12/structs_ts/src/stack.test.ts

@@ -0,0 +1,40 @@
+import { Stack } from './stack.js';
+
+describe('Stack', () => {
+  test('testPush', () => {
+    const stack = new Stack();
+    stack.push(1);
+    expect(stack.peek()).toBe(1);
+  });
+
+  test('testPop', () => {
+    const stack = new Stack();
+    stack.push(1);
+    stack.push(2);
+    expect(stack.pop()).toBe(2);
+    expect(stack.pop()).toBe(1);
+  });
+
+  test('testTop', () => {
+    const stack = new Stack();
+    stack.push(1);
+    stack.push(2);
+    expect(stack.peek()).toBe(2);
+    stack.pop();
+    expect(stack.peek()).toBe(1);
+  });
+
+  test('testIsEmpty', () => {
+    const stack = new Stack();
+    expect(stack.isEmpty()).toBe(true);
+    stack.push(1);
+    expect(stack.isEmpty()).toBe(false);
+    stack.pop();
+    expect(stack.isEmpty()).toBe(true);
+  });
+
+  test('testTopEmptyStack', () => {
+    const stack = new Stack();
+    expect(() => stack.peek()).toThrow();
+  });
+});