Running unit tests shouldn't feel like a coffee break. But on our main frontend project, that's exactly what happened. Every time we launched a single test file, we had to wait over 20 seconds before the first test even started.
We tried the usual fixes: tweaking the vitest.config.ts, isolating threads, optimizing mocks... Nothing worked. The bottleneck wasn't in the configuration—it was deep in our architecture.
In this article, I share how we used Gemini 3 Pro to identify and fix the issue, dividing our local test startup time by 5 and saving 15 minutes on every CI pipeline run.
What you'll learn in the full post
✅ The "God Module" Anti-Pattern: How importing a single utility can silently load your entire application.
✅ AI-Assisted Debugging: Why Gemini 3 Pro succeeded where other models failed to diagnose architectural flaws.
✅ The Refactoring Strategy: How we decoupled our Redux Store and Modal System to stop the dependency chain.
✅ Concrete Results: The before/after metrics that proved the fix worked.
A taste of the problem
The issue wasn't the test execution speed itself, but the transform and collect phases of Vitest.
Here is what running a single, isolated test looked like:
Test Files 1 passed (1)
Tests 3 passed (3)
Start at 09:32:08
Duration 22.53s (transform 12.53s, collect 21.47s, tests 323ms)
Notice the disconnect? 323ms to run the test, but 21+ seconds to prepare it.
The culprit? Our component imports were triggering a chain reaction. For example, importing a modal provider for a test was inadvertently importing every single modal in the application (Billing, Planning, Resources...), forcing Vitest to parse thousands of files unnecessarily.
The Fix
We used AI to refactor our architecture, splitting "heavy" UI providers from "light" contexts used in tests.
The result speaks for itself:
Duration 4.29s (transform 1.90s, setup 189ms, collect 3.44s)
If you are struggling with slow Vitest startup times or want to see how AI can help with complex architectural refactoring, check out the full story.
👉 Read the full article here: How Gemini 3 Pro cut our pipeline time in half
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