test: add test for bad practice of dependency injection

app/dependency-injection/bad-practice.spec.ts

@@ -0,0 +1,17 @@
+import { User, Order } from "./bad-practice";
+
+describe('Dependency bad practice', () => {
+  jest.spyOn(Order.prototype, 'getOrderByUser').mockImplementation((id) => {
+    return `mock order ${id}`
+  });
+
+  const user = new User();
+
+  it('should pass', () => {
+    expect(1).toBe(1);
+    const result = user.getUser(1);
+    expect(Order.prototype.getOrderByUser).toHaveBeenCalledTimes(1);
+    expect(result).toEqual('mock order 1 for user');
+
+  })
+})