Introduction to Test-Driven Development (TDD) with C# Examples
Tags: testing, programming, tdd, beginners
Published: 2023-11-29 15:30:39

## Introduction

In the dynamic realm of software development, the pursuit of impeccable code, the avoidance of pesky bugs is the ultimate quest. 
Yet, this journey is full of challenges, particularly as projects grow in complexity, this is where Test-Driven Development (TDD) emerges as your trustworthy companion. In this article, we will dive into TDD, unravel its benefits, explore how to utilize it proficiently with C# code examples, and importantly navigate the complexities of requirements and what precisely should be tested. We will look at the aspects of software that need testing, with practical testing examples on: functionality, data types, boundaries, behavior driven tests, security, performance and integration.

## The TDD Ballet

What exactly does TDD entail? Envision TDD as a choreographed dance, with you as the choreographer:

Step 1 Craft a Test: Picture building a calculator. Initially, you formulate a test case that articulates your code's intended behavior. It resembles composing the dance steps.

```csharp
[Test]
public void TestAddition()
{
    Calculator calculator = new Calculator();
    int result = calculator.Add(2, 3);
    Assert.AreEqual(5, result);
}

```
Step 2 Craft the Code: Subsequently, you script the code, ensuring it aligns with the aspirations of your test. This phase equates to instructing your dancers in the steps.

```csharp
public class Calculator
{
    public int Add(int a, int b)
    {
        return a + b;
    }
}

```
Step 3 Execute the Test: It's time to evaluate whether your code performs the dance flawlessly. Execute the tests and verify that they passed as expected.

```
$ dotnet test

```
Step 4 Refine: If the dance seems somewhat lacking in elegance, you can fine-tune it. Polish your code to make it sleeker, swifter, or more efficient. However, remember the golden rule: don't disrupt what's already working.

```csharp
public class Calculator
{
    public int Add(int a, int b)
    {
        if (a < 0)
        {
            throw new ArgumentException("Input must be non-negative", nameof(a));
        }
        return a + b;
    }
}

```
Step 5 Repeat: Continuously iterate through these steps for each new segment of the dance you intend to teach.

## Why TDD Triumphs

TDD isn't just a dance; it's a dance-off where victory is guaranteed.

####Offers

Improved code quality: TDD can unveil any missing specifications of the feature you are developing and help find bugs early in the development cycle.

Painless Maintenance: Your code becomes a breeze to maintain. Farewell to those late-night debugging expeditions.

Swift Troubleshooting: If something falters, your tests pinpoint the trouble spot. No more sifting through code like a detective in a labyrinth.

Regression Resilience: Armed with an array of tests, you can confidently introduce fresh moves without disarraying the old ones.

Living Documentation: Your tests materialize as a cheat sheet for your code. Everyone comprehends what to expect in the dance.

Team Harmony: TDD fosters cohesion among your team, developers and testers.

## What Warrants Testing in TDD

Now, let's now address the most basic question: What should be subjected to testing in TDD? Here is a thorough analysis of your software's components that demand close examination, along with real-world examples:

Functionality Testing: This represents the very essence of TDD. You assess whether your code executes its designated functions. For instance, if you consider designing a calculator you should test against the addition function.

```csharp
// Testing Calculator's Addition
[Test]
public void TestAddition()
{
    Calculator calculator = new Calculator();
    int result = calculator.Add(2, 3);
    Assert.AreEqual(5, result);
}

```
Data Type Testing: Validating data types for accuracy is essential. Ensure that the variables, inputs, and outputs you use correspond to the appropriate data type and size. This strategy works as a prevention towards data-related errors.

```csharp
// Verification of Integer Data Type
[Test]
public void TestIntegerDataType()
{
    int number = 42;
    Assert.IsInstanceOfType(number, typeof(int));
}

```
Edge Cases and Boundaries: Probe the extremities. Investigate the outcomes when you present the smallest or largest conceivable values. For instance, if your calculator can process integers, examine its behavior with the most minuscule and colossal integers.

```csharp
// Edge Cases and Boundaries, adding one to int.MaxValue should throw an OverflowException
[Test]
public void AddingOneToIntMaxValueThrowsOverflowException()
{
    int maxValue = int.MaxValue;

    Assert.Throws<OverflowException>(() =>
    {
        int result = checked(maxValue + 1);
    });
}

```
UI Testing writing it the Gherkin way: UI testing assumes paramount importance for assuring the seamless functionality of your application's user interface. Tools such as Gherkin/SpecFlow provide a framework to draft human-readable scenarios that test the behavior of your application.

```gherkin
Scenario: Successful User Login
    Given user navigates to the login page
    When inputs valid credentials
    And clicks the login button
    Then should be directed to the dashboard

```
Security Testing: Security should never be an afterthought. Investigate vulnerabilities such as SQL injection, cross-site scripting (XSS), and authentication flaws. Specialized security testing frameworks can unravel and mitigate these risks.

```csharp
// Prevention of SQL Injection
[Test]
public void TestSQLInjectionPrevention()
{
    // Simulate a SQL injection attempt
    string userInput = "'; DROP TABLE Users; --";
    bool isSafe = SecurityHelper.IsInputSafe(userInput);
    Assert.IsTrue(isSafe);
}

```
Performance and Benchmark Testing: Evaluation of your software's performance is crucial as it grows. How quickly is it able to work? Can it handle an abundance of users or data? Tools for performance testing shed light on these questions.

```csharp
// Evaluate improvement on bottleneck operation
[Params(1000, 10000)]
    public int Count;

    [Benchmark]
    public void GeneratePrimesMethod1()
    {
        GeneratePrimesMethod(Count);
    }

    [Benchmark]
    public void GeneratePrimesMethod2()
    {
        GeneratePrimesNewMethod(Count);
    }

// Method 1: Simple prime number generation
    public static void GeneratePrimesMethod(int count)
    {
        // Implementation detail
    }

// Method 2: New improved prime number generation method
    public static void GeneratePrimesNewMethod(int count)
    {
        // Implementation detail
    }

```
Integration Testing: Examine the interactions between the various parts of your software. This is especially important for complex systems with several interrelated components.

```csharp
// API Integration Test
public void TestApiIntegration()
{
    ApiClient apiClient = new ApiClient();
    ApiResponse response = apiClient.Get("https://someApi.aa/Getdata");
    Assert.AreEqual(200, response.StatusCode);
}

```
Regression Testing: As you introduce novel features or rectify defects, it's imperative to ascertain that the existing functionality remains unaffected. Execute regression tests to apprehend unintended side effects.

## Conclusion

In summary, Test-Driven Development (TDD) is your reliable ally in the realm of coding. It empowers you to create robust, bug-free software by putting tests at the forefront of your development process. With C# as your platform and a deep understanding of what aspects should undergo testing, you have the tools to engineer high-quality software. So, get ready to embark on your path to software excellence through TDD, where meticulous testing leads the way to success!