How to Build Bug-Free Applications with Claude Code

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Coding agents are incredible at writing code;

however, they do inevitably make mistakes. They overlook some piece of information, or they write convoluted code that leads to unexpected side effects.This is exactly the scenario where end-to-end tests are super useful. They don't rely on which code you ran or built, or similar;

they just run the application itself, the end product that the user actually sees. This enables you to have a robust testing system that discovers issues in the way users would experience them and helps you prevent users from seeing those issues at all by fixing them before they are discovered.In this article, I'll talk about what end-to-end tests are, why they are useful, and how you can implement them into your own application to minimize the number of bugs your users experience.This infographic highlights the main contents of this article. I'll cover: - end-to-end tests - what they are - how it was written before - how it's written now - how you can effectively run the end-to-end tests to minimize the amount of bugs in your application. Image by ChatGPT.What are E2E tests and why should you implement them?

Let's first discuss what end-to-end tests are. End-to-end tests are tests where an AI clicks through your application just as if a user clicks through it. It sees a particular screen, it decides which button to click, and clicks that button and sees what's on the next page. It can then let you know if it, for example, experiences an error after clicking a button, nothing happens after clicking a button, or just in general that the expected action does not occur.This image shows the setup of an end-to-end test. Image created by author with help of ChatGPT.Previously, it used to be so that you had to make these end-to-end tests manually, which was very tedious grunt work. Essentially, you would have to, when setting up an end-to-end test, go through each page manually and give the test the ID of the button it had to click. You also had to note down what the expected outcome was of clicking that button or performing that action on a particular page.This was, of course, naturally very tedious to set up initially because you had to go through every page, find the ID of the button you wanted to click, and so on.Even worse, however, was that these end-to-end tests had to be maintained. That means if you change the design of a page, change some logic, etc., the end-to-end tests would have to be updated, meaning having an end-to-end test would have a pretty severe maintenance cost you would have to carry for the rest of the life cycle of that end-to-end test.Luckily, with coding agents, the game has completely changed, and end-to-end tests are much faster to build and much easier to maintain.An end-to-end test is now essentially just an agent with a computer or with a browser access and a mandate/plan for what it should do. For example, it could be that you have an agent and you tell it to find its way to page A, perform action B, and the outcome C should happen.You then don't have to update the agent if the design of the page changes as long as the button is still located on each page. Furthermore, it's a lot more generalized, so the agents are able to detect issues that the previous (narrow) end-to-end tests did not discover. It's also much easier to build a bigger suite of end-to-end test agents because it's so easy to spin them up and create them, which allows you to create better test coverage for your application.···The main reason that you should implement end-to-end tests is, of course, that they discover issues before your users experience them. End-to-end tests experience the app just like a user;

the agent is typically given the same permissions and the same rules, and you can represent different users with different agents.For example, if you have a normal user and an admin user, you can have one agent for each to test their journeys, making sure both of them work, and this can essentially just be