Introduction: Why AI Unit Tests in .NET Need Help
Developers are increasingly using AI tools like GitHub Copilot or ChatGPT to generate AI unit tests in .NET projects. It’s fast, it’s easy, and it feels like magic.
But here’s the catch: most AI-generated unit tests are brittle. They fail when code evolves, miss critical edge cases, and rely on real dependencies that make tests slow or flaky.
This is why Typemock Isolator matters. By combining AI scaffolds with Typemock’s mocking power, .NET teams can move from “quick tests” to production-grade unit testing.
AI Unit Tests .NET: The Hybrid Workflow
Here’s how you can combine AI scaffolding with Typemock:
- AI scaffolds the tests.
Example: ask Copilot to “Write MSTest unit tests for OrderService.” - Typemock secures the tests.
- Fake statics like
Clock.UtcNow - Fake sealed classes like
PaymentGateway - Stub private methods for edge cases
- Prevent real network calls
- Fake statics like
- You focus on logic.
Instead of boilerplate, you test what matters: business rules, edge cases, and system behavior.
👉 Learn more about unit testing in .NET with MSTest (Microsoft Docs).
Example: Securing AI Unit Tests with Typemock
AI scaffold (fragile):
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[TestMethod] public void Place_HappyPath_ReturnsTrue() { var svc = new OrderService(new PaymentGateway(), new HttpClient()); var result = svc.Place("C-1", 100m); Assert.IsTrue(result); } |
Typemock upgrade (robust):
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Isolate.WhenCalled(() => Clock.UtcNow).WillReturn(new DateTime(2025, 01, 15)); var gateway = Isolate.Fake.Instance<PaymentGateway>(); Isolate.WhenCalled(() => gateway.Charge("C-1", 117m)).WillReturn(true); var handler = Isolate.Fake.Instance<HttpMessageHandler>(); Isolate.WhenCalled(() => handler.SendAsync(null, null)) .WillReturn(Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK))); var sut = new OrderService(gateway, new HttpClient(handler)); var ok = sut.Place("C-1", 100m); Assert.IsTrue(ok); Isolate.Verify.WasCalledWithExactArguments(() => gateway.Charge("C-1", 117m)); |
✅ No real time
✅ No real network
✅ Controlled behavior
That’s how AI unit tests in .NET become reliable.
Edge Case with Private Method
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Isolate.NonPublic.WhenCalled(sut, "CalcTax").WillReturn(5.00m); |
Failure Flow (Gateway Decline)
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Isolate.WhenCalled(() => gateway.Charge("C-3", 117m)).WillReturn(false); Isolate.Verify.WasNotCalled(() => handler.SendAsync(Isolate.Any<HttpRequestMessage>(), Isolate.Any<CancellationToken>())); |
Why Hybrid Testing Matters
- AI accelerates test creation.
- Typemock ensures correctness.
- Developers focus on edge cases.
In a modern CI/CD world (Atlassian guide), this combination means faster pipelines, fewer bugs, and higher confidence.
Conclusion
AI unit tests in .NET are a powerful accelerator, but without Typemock Isolator, they’re fragile. By combining AI scaffolding with deep mocking, you get fast, stable, and production-ready unit tests.
This is Hybrid Testing in 2025: let AI write, let Typemock secure.
👉 Try it yourself: Download Typemock
