Unit tests and TDD when code must grow without breaking what already works
This category treats .NET testing for what it really is: a way to protect margin, speed, and quality of change, not a moral ritual bolted on at the end of a project.
Analyses, cases, and articles on automated testing, TDD, and code quality
1 articles found
When testing becomes essential
Testing becomes essential when software must evolve over time, when multiple developers work on the same codebase, and when a defect can block business operations. In these scenarios tests are not optional overhead: they are the system that makes refactoring, new features, and continuous releases trustworthy.
Useful .NET technologies for testing
C#
language in which both tests and the code under test are written
.NET
platform with native support for xUnit, NUnit and MSTest
ASP.NET
the framework where integration testing is most critical
Blazor
UI components that require dedicated testing strategies
Entity Framework
ORM that should be tested with in-memory or SQLite for isolation
Sources and references
Martin Fowler, Refactoring
Fowler's book on refactoring is inseparable from testing: without tests, refactoring is a high-risk operation. I cite it here because the real reason to write tests is to be able to change code with confidence. Fowler shows how the two concepts amplify each other, and understanding this connection changes the motivation behind writing tests.
Robert C. Martin, Clean Code
Martin dedicates an important section of Clean Code to testing principles: readable tests, single assertion per test, FIRST (Fast, Independent, Repeatable, Self-validating, Timely). I cite it because in practice the problem with testing is never technical, it is almost always cultural and organizational. And Martin addresses that aspect directly.
Frequently asked questions
Unit tests verify a single unit of logic in isolation, without real external dependencies. Integration tests verify that multiple components work correctly together, including databases, HTTP services, or file systems. End-to-end tests simulate real user behavior on the complete system. The ideal ratio is: many unit tests, some integration tests, few e2e tests.
TDD, Test-Driven Development, is an approach where you write the test before the code, then write the minimum code to make it pass, then refactor. It is worth adopting when the logic is complex, requirements are clear, and you want emergent design with low dependencies. It is not suitable for fast prototypes, infrastructure code, or UI. The discipline has an upfront cost that pays off in maintenance.
xUnit is the most widely used framework in new .NET projects for its simplicity and compatibility with modern conventions. NUnit is a valid alternative with syntax closer to JUnit. MSTest is integrated into Visual Studio and is convenient for teams that heavily use the Microsoft IDE. The .NET equivalent of Mockito is Moq or NSubstitute for creating mocks.
External dependencies are handled with mocks (Moq, NSubstitute) in unit tests to isolate logic, and with test containers (Testcontainers for .NET) or in-memory databases in integration tests to verify real behavior. For HTTP APIs, WireMock.Net or custom HttpMessageHandlers are used. The principle is not to substitute the code under test, but to control its dependencies.