[Fact] // Fast: No dependency on external resources, executes quickly
public void Add_Input1And2_ShouldReturn3()
{
    // In-memory operation only, no I/O or network latency
    var calculator = new Calculator();
    var result = calculator.Add(1, 2);
    Assert.Equal(3, result);
}

[Fact] // Independent: Each test creates a new instance
public void Increment_StartFrom0_ShouldReturn1()
{
    var counter = new Counter(); // Each test creates a new instance, unaffected by other tests
    counter.Increment();
    Assert.Equal(1, counter.Value);
}

[Fact] // Repeatable: Produces the same result every execution
public void Increment_MultipleExecutions_ShouldProduceConsistentResults()
{
    var counter = new Counter();
    counter.Increment();
    counter.Increment();
    counter.Increment();
    
    // This test will produce the same result every time it runs
    Assert.Equal(3, counter.Value);
}

[Fact] // Self-Validating: Explicit verification
public void IsValidEmail_InputValidEmail_ShouldReturnTrue()
{
    var emailHelper = new EmailHelper();
    var result = emailHelper.IsValidEmail("test@example.com");
    
    Assert.True(result); // Clear pass or fail
}

[Fact]
public void Add_InputNegativeAndPositiveNumbers_ShouldReturnCorrectResult()
{
    // Arrange - Prepare test data and dependent objects
    var calculator = new Calculator();
    const int a = -5;
    const int b = 3;
    const int expected = -2;

    // Act - Execute the method under test
    var result = calculator.Add(a, b);

    // Assert - Verify if the result meets expectations
    Assert.Equal(expected, result);
}

[MethodUnderTest]_[TestScenario]_[ExpectedBehavior]

[Fact]
public void Add_Input0And0_ShouldReturn0()
{
    var calculator = new Calculator();
    var result = calculator.Add(0, 0);
    Assert.Equal(0, result);
}

[Theory]
[InlineData(1, 2, 3)]
[InlineData(-1, 1, 0)]
[InlineData(0, 0, 0)]
[InlineData(100, -50, 50)]
public void Add_InputVariousNumberCombinations_ShouldReturnCorrectResult(int a, int b, int expected)
{
    var calculator = new Calculator();
    var result = calculator.Add(a, b);
    Assert.Equal(expected, result);
}

[Theory]
[InlineData("invalid-email")]
[InlineData("@example.com")]
[InlineData("test@")]
[InlineData("test.example.com")]
public void IsValidEmail_InputInvalidEmailFormats_ShouldReturnFalse(string invalidEmail)
{
    var emailHelper = new EmailHelper();
    var result = emailHelper.IsValidEmail(invalidEmail);
    Assert.False(result);
}

[Fact]
public void Divide_Input10And0_ShouldThrowDivideByZeroException()
{
    // Arrange
    var calculator = new Calculator();
    const decimal dividend = 10m;
    const decimal divisor = 0m;

    // Act & Assert
    var exception = Assert.Throws<DivideByZeroException>(
        () => calculator.Divide(dividend, divisor)
    );

    // Verify exception message
    Assert.Equal("Divisor cannot be zero", exception.Message);
}

Solution/
├── src/
│   └── MyProject/
│       ├── Calculator.cs
│       └── MyProject.csproj
└── tests/
    └── MyProject.Tests/
        ├── CalculatorTests.cs
        └── MyProject.Tests.csproj

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <TargetFramework>net9.0</TargetFramework>
        <ImplicitUsings>enable</ImplicitUsings>
        <Nullable>enable</Nullable>
        <IsPackable>false</IsPackable>
    </PropertyGroup>

    <ItemGroup>
        <PackageReference Include="coverlet.collector" Version="6.0.4">
            <PrivateAssets>all</PrivateAssets>
            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
        </PackageReference>
        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
        <PackageReference Include="xunit" Version="2.9.3" />
        <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
            <PrivateAssets>all</PrivateAssets>
            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
        </PackageReference>
    </ItemGroup>

    <ItemGroup>
        <Using Include="Xunit" />
    </ItemGroup>

    <ItemGroup>
        <ProjectReference Include="..\..\src\MyProject\MyProject.csproj" />
    </ItemGroup>

</Project>