Don't Trust Your Stub. Trust the Transcript.

Wed, 09 Sep 2026 13:41:53 +0000

Ticket stubs

See the accompanying code repo on Github here.

The Stub That Used to Be True

Here’s a test that used to live in ShopApp, the companion project for this series of articles.

@Test("fetchProducts decodes the remote response")
func fetchProductsDecodesResponse() async throws {
 let client = MockNetworkClient()
 try client.setJSON(StoreProduct.stubs)
 let repo = DefaultStoreRepository(client: client)
 let products = try await repo.fetchProducts(category: nil)
 #expect(products.count == StoreProduct.stubs.count)
}

This is the standard for a reliable unit test — explicit state, fast feedback, no simulator required. It loads a stubbed response object — a Swift array standing in for what the API returns. It was testing that the repository decodes a JSON array into StoreProduct values, that caching works, and that the URL gets built right. It was not checking that StoreProduct.stubs return what the actual server response is. The stubs were written by a coding agent against the API contract at the time it was defined in the spec.

AI Writes Fast. Your Safety Net Needs to Be Faster.

Sat, 01 Aug 2026 12:37:28 +0000

I’ve been writing code for the past year switching between Copilot, Claude Code and Codex (sorry Cursor, it just didn’t happen). With these tools, building a flow of screens for an app — the UI, the model, a first pass at test coverage — takes minutes instead of days.

What hasn’t gotten any faster is what happens next: the review process of the code changes before merging it into a large, live production project. It has to be manually reviewed line by line. Am I confident that an agent-generated PR is correct? Definitely not. It generates plausible code that compiles, but often has a subtle change that isn’t correct. In general, the higher velocity output in generated code has led to more bugs — AI-generated code creates 1.7x more problems than human-written code, per CodeRabbit’s analysis.

Testing on Ronan O Ciosoig

Don't Trust Your Stub. Trust the Transcript.

The Stub That Used to Be True

AI Writes Fast. Your Safety Net Needs to Be Faster.