# Unit Testing & xUnit (.NET)

> xUnit framework, test cases, assertions, Moq, FluentAssertions, code coverage, TDD principles

- 20 interview questions
- Mid-Level
- [Interview Questions: .NET](https://sharpskill.dev/en/technologies/dotnet/interview-questions.md)

## 1. What is xUnit in the context of .NET?

**Answer**

xUnit is an open-source unit testing framework for .NET, inspired by JUnit and NUnit. It uses attributes like [Fact] for simple tests and [Theory] for parameterized tests. xUnit encourages best practices like test isolation (each test creates a new test class instance) and avoids shared state via traditional Setup/Teardown methods.

## 2. What is the difference between [Fact] and [Theory] in xUnit?

**Answer**

[Fact] decorates a simple test that runs once without parameters, while [Theory] decorates a parameterized test that runs multiple times with different values provided via [InlineData], [MemberData], or [ClassData]. Using [Theory] avoids code duplication when testing multiple similar scenarios with different data.

## 3. How to use [InlineData] with [Theory] in xUnit?

**Answer**

[InlineData] provides data directly in the attribute for a [Theory] test, allowing the same test to run with different values. Each [InlineData] attribute represents a distinct test case. This approach is ideal for testing multiple simple scenarios without creating separate data classes, reducing boilerplate code.

## 17 more questions available

- What is the main advantage of Moq in .NET unit testing?
- How to configure a mock with Moq so that a method returns a specific value?

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