Interview Q&A

Short answer: xUnit encourages constructor injection for setup instead of [SetUp] methods. It uses [Fact] and [Theory] attributes for test methods, while NUnit/MSTest use [Test] and [TestMethod]. xUnit does not use [TestInitialize]/[TestCleanup] but favors class fixtures and constructor/dispose patterns. xUnit is better integrated with .NET Core and supports parallel test execution by default.

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: [Fact]: Defines a parameterless test method representing a single test case. [Theory]: Defines a parameterized test that runs multiple times with different data inputs, provided by [InlineData] or other data sources.

Real-world example (ShopNest)

Arrange a cart with 2 items → Act Checkout() → Assert total and that payment was called once.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Using [Theory] and data attributes like [InlineData]: [Theory] [InlineData(2, 3, 5)] [InlineData(10, 20, 30)] public void Add_ReturnsSum(int a, int b, int expected) { var calculator = new Calculator(); var result = calculator.Add(a, b); Assert.Equal(expected, result); }

Example code

Using [Theory] and data attributes like [InlineData]: [Theory] [InlineData(2, 3, 5)] [InlineData(10, 20, 30)] public void Add_ReturnsSum(int a, int b, int expected)
{
var calculator = new Calculator();
var result = calculator.Add(a, b); Assert.Equal(expected, result); }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the constructor for setup code. Implement IDisposable interface for teardown (cleanup) code. Example: public class DatabaseTests : IDisposable

Example code

{
public DatabaseTests()
{ // Setup } [Fact] public void TestMethod() { }
public void Dispose()
{ // Cleanup }
}
For shared context across multiple tests, use class fixtures or collection fixtures.

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the Skip property on [Fact] or [Theory]: [Fact(Skip = "Reason for skipping")] public void SkippedTest() { }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Group related tests in the same class. Use Collection attribute to group classes that share setup/teardown or should not run in parallel. [Collection("Database collection")] public class TestClass1 { } [Collection("Database collection")] public class TestClass2 { }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Test fixtures provide a way to share setup and cleanup code between tests. xUnit supports: Class Fixtures: Shared across all tests in a class. Collection Fixtures: Shared across multiple test classes. They are implemented by creating a fixture class and injecting it into test classes via constructor.

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the dotnet test CLI command: dotnet test YourTestProject.csproj This runs all tests in the project and outputs results in the console. Additional options allow filtering and outputting reports. NUnit Framework

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: NUnit uses [Test] for test methods, whereas xUnit uses [Fact]. NUnit uses [SetUp] and [TearDown] for setup and cleanup, while xUnit uses constructors and IDisposable. NUnit supports [TestCase] for parameterized tests, xUnit uses [Theory] with [InlineData]. NUnit has more built-in attributes like [Category] for grouping tests.

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: [TestCase(2, 3, 5)] [TestCase(10, 20, 30)] public void Add_ReturnsSum(int a, int b, int expected)

Example code

{
var calculator = new Calculator();
var result = calculator.Add(a, b); Assert.AreEqual(expected, result); }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: [Test] public void Divide_ByZero_ThrowsException()

Example code

{
var calculator = new Calculator(); Assert.Throws<DivideByZeroException>(() => calculator.Divide(10, 0)); }

Real-world example (ShopNest)

Arrange a cart with 2 items → Act Checkout() → Assert total and that payment was called once.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the [Category("CategoryName")] attribute to group tests, allowing filtering by category during test runs. [Test, Category("Integration")] public void IntegrationTest() { }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use [Ignore("Reason")] to skip tests unconditionally, or [Category] combined with test runner filters. For conditional ignoring, you can use Assume statements or custom logic inside tests.

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Download and use nunit3-console.exe from NUnit site: nunit3-console.exe YourTestAssembly.dll It runs all tests in the assembly and outputs results.

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Yes, NUnit integrates seamlessly with CI/CD tools like Azure DevOps, Jenkins, GitHub Actions, and others using command-line runners or plugins, allowing automated test execution during builds and deployments. MSTest Framework

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: [TestClass] public class CalculatorTests { [TestMethod] public void Add_ReturnsSum()

Example code

{
var calculator = new Calculator();
var result = calculator.Add(2, 3); Assert.AreEqual(5, result); }
}

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: MSTest is Microsoft's official framework; NUnit and xUnit are community-driven. MSTest uses [TestClass] and [TestMethod] attributes; xUnit uses [Fact], NUnit uses [Test]. MSTest has less flexibility in data-driven tests compared to NUnit’s [TestCase] and xUnit’s [Theory]. xUnit promotes constructor-based setup, MSTest uses [TestInitialize].

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: ttributes? [TestInitialize] runs code before each test method to set up prerequisites. [TestCleanup] runs after each test method to clean up resources. [TestInitialize] public void Setup() { /* setup code */ } [TestCleanup] public void Cleanup() { /* cleanup code */ }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: [TestInitialize] runs code before each test method to set up prerequisites. [TestCleanup] runs after each test method to clean up resources. [TestInitialize] public void Setup() { /* setup code */ } [TestCleanup] public void Cleanup() { /* cleanup code */ }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: [TestMethod] [ExpectedException(typeof(DivideByZeroException))] public void Divide_ByZero_ThrowsException()

Example code

{
var calculator = new Calculator(); calculator.Divide(10, 0); }

Real-world example (ShopNest)

Arrange a cart with 2 items → Act Checkout() → Assert total and that payment was called once.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: How? Yes, MSTest supports data-driven tests using [DataTestMethod] and [DataRow] attributes: [DataTestMethod] [DataRow(2, 3, 5)] [DataRow(10, 20, 30)] public void Add_ReturnsSum(int a, int b, int expected)

Example code

{
var calculator = new Calculator();
var result = calculator.Add(a, b); Assert.AreEqual(expected, result); }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Yes, MSTest supports data-driven tests using [DataTestMethod] and [DataRow] ttributes: [DataTestMethod] [DataRow(2, 3, 5)] [DataRow(10, 20, 30)] public void Add_ReturnsSum(int a, int b, int expected) { var calculator = new Calculator(); var result = calculator.Add(a, b); ssert.AreEqual(expected, result); } Yes, MSTest supports data-driven tests using… [DataTestMethod] and [DataRow] ttributes: [DataTestMethod]…

Explain a bit more

[DataRow(2, 3, 5)] [DataRow(10, 20, 30)] public void Add_ReturnsSum(int a, int b, int expected) { var calculator = new Calculator(); var result = calculator.Add(a, b); ssert.AreEqual(expected, result); }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the [TestCategory("CategoryName")] attribute to group tests for filtering. [TestMethod] [TestCategory("Integration")] public void IntegrationTest() { }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the [Ignore("Reason")] attribute on the test method or class. [Ignore("Test is temporarily disabled")] [TestMethod] public void SkippedTest() { }

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use dotnet test CLI for .NET Core MSTest projects: dotnet test YourTestProject.csproj In Azure DevOps, use the Visual Studio Test task or the DotNetCoreCLI task to run tests during builds and releases.

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.