Tests in same project

.gitignore

bin/
obj/
.vs/
.idea/
.vscode/
*.user

Calculator.cs

namespace TestsInSameProject;

class Calculator
{
    public int Add(int x, int y) => x + y;
}

CalculatorTests.cs

using Xunit;

namespace TestsInSameProject;

public class CalculatorTests
{
    [Theory]
    [InlineData(1, 2, 3)]
    [InlineData(1, 0, 1)]
    [InlineData(0, 0, 0)]
    [InlineData(1, -2, -1)]
    public void Add_Returns_Sum_Of_Arguments(int x, int y, int expected)
    {
        var calculator = new Calculator();
        var actual = calculator.Add(x, y);
        Assert.Equal(expected, actual);
    }
}

global.json

{
  "sdk": {
    "version": "6.0.402"
  }
}

Program.cs

using TestsInSameProject;

if (args.Length < 2)
{
    Console.Error.WriteLine("Missing arguments");
    return 1;
}

int x = int.Parse(args[0]);
int y = int.Parse(args[1]);
var calculator = new Calculator();
int result = calculator.Add(x, y);
Console.WriteLine(result);

return 0;

TestsInSameProject.csproj

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

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup Condition="$(StripTests) != 'true'">
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
    <PackageReference Include="xunit" Version="2.4.2" />
    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
  </ItemGroup>

  <ItemGroup Condition="$(StripTests) == 'true'">
    <Compile Remove="**/*Tests.cs" />
  </ItemGroup>

</Project>