Question 1

How do OOP principles show up in a C# automation framework?

Accepted Answer

Page classes encapsulate locators behind methods, test classes inherit a BaseTest for setup/teardown, IWebDriver gives polymorphism across browsers, and interfaces/abstract classes provide abstraction.

Question 2

What is the difference between value types and reference types?

Accepted Answer

Value types (int, bool, struct, enum) hold their data directly and are copied on assignment. Reference types (class, string, arrays, interfaces) hold a reference to an object, so copies point to the same instance.

Question 3

What are properties and auto-properties in C#?

Accepted Answer

Properties expose fields through get/set accessors with optional logic, and auto-properties let the compiler generate the backing field. In page objects, expression-bodied properties are a clean way to expose elements.

Question 4

Interface vs abstract class in C#?

Accepted Answer

A class can implement many interfaces but inherit only one abstract class. Abstract classes can have fields, constructors and implemented members; interfaces define contracts and since C# 8 can include default implementations.

Question 5

string vs StringBuilder in C#?

Accepted Answer

string is immutable, so each concatenation creates a new object. StringBuilder is mutable and efficient when building strings in loops, such as large logs or report bodies.

Question 6

How do you handle exceptions in C# test code?

Accepted Answer

Use try/catch for specific exceptions, finally for cleanup, and exception filters with when for conditional handling. In tests, let unexpected exceptions fail the test and use Assert.Throws to verify expected ones.

Question 7

Which collections do you use in C# automation?

Accepted Answer

List for ordered items, Dictionary for test data and config, HashSet for uniqueness, and ReadOnlyCollection which Selenium's FindElements returns.

Question 8

How do you use LINQ in test automation?

Accepted Answer

LINQ queries collections declaratively with Select, Where, OrderBy, Any and more. It's ideal for extracting element text, validating sort order and filtering API response data.

Question 9

Explain async/await and why it matters for Playwright .NET.

Accepted Answer

async/await lets methods run asynchronous I/O without blocking threads; await pauses until the Task completes. Playwright .NET's API is fully async, so tests and page objects return Task and await every call.

Question 10

Compare NUnit, xUnit and MSTest.

Accepted Answer

All three are .NET test frameworks. NUnit uses [Test], [SetUp], [TestCase] and is most common for Selenium; xUnit uses [Fact]/[Theory] with constructor/IDisposable for setup; MSTest uses [TestMethod], [TestInitialize] and [DataRow].

Question 11

How do you manage driver setup and teardown in NUnit?

Accepted Answer

Create the driver in [SetUp] and quit it in [TearDown] in a BaseTest class. For parallel runs, store it in ThreadLocal<IWebDriver> or use [FixtureLifeCycle(LifeCycle.InstancePerTestCase)].

Question 12

How do you implement explicit waits in Selenium C#?

Accepted Answer

Use WebDriverWait with a lambda condition, since ExpectedConditions moved out of the core package. Configure IgnoreExceptionTypes for transient exceptions.

Question 13

How do you write tests with Playwright for .NET?

Accepted Answer

Install Microsoft.Playwright.NUnit (or MSTest/xUnit), inherit PageTest to get a Page per test, and use async locators with auto-waiting plus Expect() web-first assertions.

Question 14

How do you manage configuration and dependency injection in a .NET test framework?

Accepted Answer

Load settings from appsettings.json and environment variables with Microsoft.Extensions.Configuration, bind them to a typed class, and register services like driver factories and API clients in a DI container.

Question 15

What is Reqnroll (SpecFlow) and how does BDD work in C#?

Accepted Answer

Reqnroll is the open-source successor to SpecFlow, which reached end of life. Gherkin feature files describe behavior and step definition classes bind each Given/When/Then to C# methods, running on NUnit, xUnit or MSTest.

Question 16

How do you make WebDriver thread-safe for parallel NUnit runs?

Accepted Answer

Store the driver in ThreadLocal<IWebDriver> (or use InstancePerTestCase fixtures) so each parallel test gets its own browser. Create it in [SetUp] and quit and clear it in [TearDown].

Question 17

Reverse a string without using built-in Reverse.

Accepted Answer

Convert to a char array and swap characters from both ends with two pointers, then build a new string. It runs in O(n) time.

Question 18

Find duplicate elements in an array using a HashSet or LINQ.

Accepted Answer

Use a HashSet and collect items where Add returns false, which is O(n). LINQ GroupBy with Count() > 1 is a concise alternative.

Question 19

Check if a string is a palindrome.

Accepted Answer

Filter to letters/digits, lowercase, then compare characters from both ends moving inward. Return false on the first mismatch.

Question 20

Count character frequency with a Dictionary and find the first non-repeating character.

Accepted Answer

Loop through characters and increment counts in a Dictionary<char,int>. Then scan the original string and return the first character whose count is 1.

Question 21

What are .NET, the CLR and IL, and how does C# code run?

Accepted Answer

The C# compiler turns source code into Intermediate Language (IL) stored in assemblies (.dll). At runtime the Common Language Runtime (CLR) JIT-compiles IL into native code and provides garbage collection, type safety and exception handling.

Question 22

What is the difference between var, const and readonly in C#?

Accepted Answer

var lets the compiler infer a local variable's type, but it's still statically typed. const is a compile-time constant that must be assigned in the declaration, while readonly fields can be assigned in the declaration or constructor and are fixed after that.

Question 23

What do the ref, out and in parameter modifiers do?

Accepted Answer

All three pass arguments by reference. ref requires the variable to be initialized and lets the method change it, out doesn't need initialization but the method must assign it, and in passes by reference as read-only.

Question 24

What are nullable value types and nullable reference types in C#?

Accepted Answer

int? is a nullable value type (Nullable) that can hold null. Nullable reference types, enabled with enable, make string mean non-null and string? mean may-be-null, so the compiler warns about possible null dereferences.

Question 25

How do string interpolation and string comparison work in C#?

Accepted Answer

Interpolated strings use $"...{expr}..." to embed values, and verbatim strings @"..." keep backslashes literally. Unlike Java, == on strings compares content, and string.Equals with StringComparison controls case sensitivity.

Question 26

What is the difference between an array and List<T> in C#?

Accepted Answer

An array has a fixed length set at creation, while List is a resizable generic collection backed by an array that grows as you add items. Both support indexing; List adds Add, Remove, Contains and Find.

Question 27

What is a static class and when do you use static members in a C# framework?

Accepted Answer

A static class can't be instantiated or inherited and contains only static members, which makes it suitable for helpers and extension methods. Static members belong to the type rather than an instance and are shared across all callers.

Question 28

Explain C# access modifiers including internal and protected internal.

Accepted Answer

public is visible everywhere and private only within the type. protected adds derived classes, internal limits access to the same assembly, protected internal is internal OR derived, and private protected is derived classes within the same assembly.

Question 29

Write FizzBuzz in C# using a switch expression.

Accepted Answer

Loop from 1 to n and map each number with a switch on a tuple of (i % 3, i % 5). The pattern (0, 0) gives FizzBuzz, (0, _) Fizz, (_, 0) Buzz and anything else the number itself.

Question 30

Generate the Fibonacci series in C# using yield return.

Accepted Answer

Keep two running values and yield each one, then update with tuple assignment (a, b) = (b, a + b). yield return produces an IEnumerable lazily, so callers can Take(n) as many terms as needed.

Question 31

Check if a number is prime in C# and list primes with LINQ.

Accepted Answer

Return false below 2, handle even numbers, then check odd divisors up to the square root. Enumerable.Range combined with Where(IsPrime) lists primes in a range.

Question 32

What is boxing and unboxing in C#?

Accepted Answer

Boxing wraps a value type in an object on the heap, for example assigning an int to an object variable. Unboxing extracts it back with an explicit cast, and the cast must match the exact boxed type.

Question 33

What is the difference between class, struct and record in C#?

Accepted Answer

A class is a reference type with reference equality by default. A struct is a value type copied on assignment, suited to small data. A record (class or struct) provides value-based equality, immutability helpers and a readable ToString, which is ideal for test data and DTOs.

Question 34

What are delegates, Func, Action and events?

Accepted Answer

A delegate is a type-safe reference to a method. Func returns a value, Action returns void and Predicate returns bool, and an event is a delegate that outside code can only subscribe to, not invoke.

Question 35

What are extension methods and how do you use them in a test framework?

Accepted Answer

Extension methods add methods to existing types without modifying them; they're static methods in a static class whose first parameter uses the this modifier. They're great for helpers like driver.WaitForVisible(locator).

Question 36

How do generics and generic constraints work in C#?

Accepted Answer

Generics let you write type-safe reusable code with type parameters like <T>. Constraints with where restrict T, for example where T : BasePage or where T : new(), so you can call its members or create instances safely.

Question 37

What is deferred execution in LINQ, and how do IEnumerable, IQueryable and List differ?

Accepted Answer

Most LINQ operators are deferred: the query runs only when you enumerate it, and re-runs each time. IEnumerable executes in memory, IQueryable builds an expression tree translated by a provider like EF Core into SQL, and ToList() executes immediately and caches results.

Question 38

What is IDisposable and how does the using statement work?

Accepted Answer

IDisposable defines Dispose() for releasing unmanaged or expensive resources deterministically. A using statement or declaration calls Dispose automatically when the scope ends, even if an exception occurs.

Question 39

How does garbage collection work in .NET?

Accepted Answer

The .NET GC is generational: new objects start in Gen 0, survivors are promoted to Gen 1 and Gen 2, and young generations are collected more often because most objects die young. Large objects (85,000 bytes or more) go to the Large Object Heap.

Question 40

How do xUnit test lifecycles and fixtures work?

Accepted Answer

xUnit creates a new test class instance per test, so the constructor is setup and Dispose is teardown. For shared expensive setup, IClassFixture shares an object across tests in one class and ICollectionFixture shares it across classes in a collection.

Question 41

How do you write data-driven tests in NUnit?

Accepted Answer

Use [TestCase] for inline argument sets, [TestCaseSource] to pull cases from a static method or property, and [Values]/[Range] for combinations. Each case appears as a separate test in the results.

Question 42

Check whether two strings are anagrams in C#.

Accepted Answer

Normalize both strings, then compare their sorted characters with SequenceEqual, which is O(n log n). An int[26] or Dictionary counting approach is O(n).

Question 43

Find the second highest number in an int array in C#.

Accepted Answer

Track the largest and second largest in one loop, skipping values equal to the largest, and return null if there's no second distinct value. The LINQ version is Distinct().OrderByDescending(x => x).Skip(1).FirstOrDefault().

Question 44

Find the missing number in an array of 1 to n in C#.

Accepted Answer

Compute n * (n + 1) / 2 and subtract the array's Sum(). For several missing values, use Enumerable.Range(1, n).Except(array).

Question 45

How do you run async work in parallel with Task.WhenAll, and how do you avoid async deadlocks?

Accepted Answer

Start all tasks first, then await Task.WhenAll so they run concurrently and you get every result or the first exception. Avoid blocking on async code with .Result or .Wait(), which can deadlock in environments with a synchronization context and wastes threads elsewhere.

Question 46

How do you make shared state thread-safe in parallel C# tests?

Accepted Answer

Avoid shared mutable state where possible; otherwise protect it with lock, use atomic operations from Interlocked, or use concurrent collections like ConcurrentDictionary and ConcurrentBag. For per-test state such as drivers, use instance fields, AsyncLocal or ThreadLocal.

Question 47

Which C# 10–12 features do you use in automation code?

Accepted Answer

Useful ones include file-scoped namespaces and global usings (C# 10), raw string literals and required members (C# 11), and primary constructors and collection expressions (C# 12). They cut boilerplate in page objects and test data.

Question 48

How does pattern matching work in modern C#?

Accepted Answer

Pattern matching tests a value against a shape and extracts data in one step. C# supports type patterns, property patterns, relational patterns (> 500), logical patterns (and, or, not) and list patterns, usable in is expressions and switch expressions.

Question 49

How do custom attributes and reflection work in C# test frameworks?

Accepted Answer

Attributes attach metadata to code, and reflection reads it at runtime; that's how NUnit discovers [Test] and [TestCase]. You can define your own attribute, like [JiraId("QA-123")], and read it in a hook to link results to test management.

Question 50

Sort an integer array in C# without Array.Sort or LINQ OrderBy.

Accepted Answer

Use bubble sort: compare adjacent elements and swap when out of order, shrinking the unsorted range each pass and stopping early if nothing swapped. Tuple swap syntax keeps it concise; complexity is O(n^2).

Interview Questions

01How do OOP principles show up in a C# automation framework?BeginnerC# Fundamentals

02What is the difference between value types and reference types?BeginnerC# Fundamentals

03What are properties and auto-properties in C#?BeginnerC# Fundamentals

04Interface vs abstract class in C#?BeginnerC# Fundamentals

05string vs StringBuilder in C#?BeginnerC# Fundamentals

06How do you handle exceptions in C# test code?BeginnerC# Fundamentals

07Which collections do you use in C# automation?BeginnerC# Fundamentals

08How do you use LINQ in test automation?IntermediateLINQ & Async

09Explain async/await and why it matters for Playwright .NET.IntermediateLINQ & Async

10Compare NUnit, xUnit and MSTest.IntermediateTest Frameworks

11How do you manage driver setup and teardown in NUnit?IntermediateTest Frameworks

12How do you implement explicit waits in Selenium C#?IntermediateSelenium & Playwright .NET

13How do you write tests with Playwright for .NET?IntermediateSelenium & Playwright .NET

14How do you manage configuration and dependency injection in a .NET test framework?IntermediateTest Frameworks

15What is Reqnroll (SpecFlow) and how does BDD work in C#?AdvancedSelenium & Playwright .NET