A single .NET Core project to rule them all


Tags: C#


The code is here.

Thanks to Mike for reviewing this.

I have always been mildly irritated by how many .net projects I need to create in my standard workflow.

Usually I start with an idea for a library; I then want to test it with a simple executable; write some XUnit tests for it and finally benchmark some key scenarios. So I end up with at least four projects to manage.

Sure, I can find ways to automatically generate those projects, but I have always been weary of codegen to solve complexity issues. It always ends up coming back to bite you. For those of you as old as I am, think MFC

So what is my ideal world then? Well, let’s try this:

  1. One single project for the library and related artifacts (i.e. test, benchmarks, etc…).
  2. Distinguish the library code from the test code from the benchmark code by some convention (i.e. name scheme).
  3. Generate each artifact (i.e. library, tests, benchmarks, executable) by passing different options to dotnet build and dotnet run.
  4. Create a new project by using the standard dotnet new syntax.
  5. Have intellisense working normally in each file for my chosen editor (VSCode).
  6. Work with dotnet watch so that one can automatically run tests when anything changes.


What follows, despite working fine, is not the standard way .net tools are used. It is not in the ‘golden path’. That is problematic for production usage as:

  1. It might not work in your particular configuration.
  2. It might not work with other tools that rely on the presence of multiple projects (i.e. code coverage? …).
  3. It might work now in all scenarios, but get broken in the future as you update to a new framework, sdk, editor.
  4. It might expose bugs in the tools, now or later, which aren’t going to be fixed, as you are not using the tools as intended.
  5. It might upset your coworkers that are used to a more standard setup.

I need to write a blog post about the concept of the ‘golden path’ and the perils, mostly hidden, of getting away from it. The summary, it is a bad idea.

Having said all of that, for the daring souls, here is one way to achieve most of the above. It also works out as a tutorial on how the different components of the .NET Core build system interacts.

How to use it

Here are the steps:

  1. Type dotnet new -i Lucabol.SingleSourceProject.
  2. Create a directory for your project and cd to it.
  3. Type dotnet new lsingleproject and optionally --standardVersion <netstandardXX> --appVersion <netcoreappXX>.
  4. Either modify the Library.cs, Main.cs, Test.cs, Bench.cs files or create your own with this convention:
    • Code for the executable goes in potentially multiple files named XXXMain.cs (i.e. MyLibrary.Main.cs).
    • Code for the tests goes into files named XXXTest.cs (i.e. MyLibrary.Test.cs).
    • Code for the benchmarks goes into files named XXXBench.cs (i.e. MyLibrary.Bench.cs).
    • Any .cs file not following the above conventions is compiled into the dll.
  5. Type:
    • dotnet build or dotnet build -c release to build debug or release version of your dll. This doesn’t include any of the main, test or bench code.
    • dotnet build -c main or dotnet build -c main_release and the corresponding dotnet run -c .. build and run the exe.
    • dotnet build -c test, dotnet build -c test_release and dotnet test -c test build and run the tests.
    • dotnet build -c bench, dotnet run -c bench build and run the benchmark.

How it all works

The various steps above are implemented as follows:

dotnet new -i ... install a custom template that I have created and pushed on NuGet.

The custom template is composed of the following files:

Code files

There is one file for each kind of artifact that the project can generate: library, program, tests and benchmark. The files follow the name terminating conventions, as described above.

Project file

The project file is identical to any other project file generated by dotnet new except that there is one additional line appended at the end:

<Import Project="Base.targets" />

This instruct msbuild to include the Base.targets file. That file has most of the magick. I have separated it out so that you can use it unchanged in your own projects.


We start by removing all the file from compilation except the ones that are used to build the library.

    <Compile Remove="**/*Bench.cs;**/*Test.cs;**/*Main.cs" />

We then conditionally include the correct ones depending on which configuration is chosen. Please notice the last line, which instruct dotnet watch to watch all the .cs files. By default it just watches the ones in the debug configuration.

    <Compile Include="**/*Test.cs"  Condition="'$(Configuration)'=='Test'"/>
    <Compile Include="**/*Test.cs"  Condition="'$(Configuration)'=='Test_Release'"/>
    <Compile Include="**/*Bench.cs" Condition="'$(Configuration)'=='Bench'"/>
    <Compile Include="**/*Main.cs"  Condition="'$(Configuration)'=='Main'"/>
    <Compile Include="**/*Main.cs"  Condition="'$(Configuration)'=='Main_Release'"/>
    <Watch Include="**\*.cs" />

Then we need to define the references. Depending on what you are building you need to include references to the correct NuGet packages (i.e. if you are building test you need the xunit packages). This is done below:

  <ItemGroup  Condition="'$(Configuration)'=='Bench' OR '$(Configuration)'=='Debug'">
    <PackageReference Include="BenchmarkDotNet" Version="0.11.3" />

  <ItemGroup Condition="'$(Configuration)'=='Test' OR '$(Configuration)'=='Test_Release' OR '$(Configuration)'=='Debug'">
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
    <PackageReference Include="xunit" Version="2.4.0" />
    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />

One thing to notice is that most references are also included in the debug configuration. This is not a good thing, but it is the only way to get VSCode Intellisense to work for all the files in the solution. Apparently, IntelliSense uses whatever reference are defined for the debug build in VsCode. So debug is special, if you wish …

But that’s not enough. When you create your own MsBuild configurations, you also have to replicate the properties and constants that are set in the debug and release configurations. You would like a way to inherit them, but I don’t think it is possible.

It is particularly important to set the TargetFramework property, as it needs to be set to netcoreappXXX for the main, test and benchmark configurations. I give an example of the Test and Test_release configurations below. The rest is similar:

  <PropertyGroup Condition="'$(Configuration)'=='Test'">

  <PropertyGroup Condition="'$(Configuration)'=='Test_Release'">

The .template.config/template.json file

This is necessary to create a dotnet new custom template. The only thing to notice is the two parameters standardVersion and appVersion that gives the user a way to indicate which version of the .NET Standard to use for the library and which version of the application framework to use for Main, Test and Bench.

  "$schema": "http://json.schemastore.org/template",
  "author": "Luca Bolognese",
  "classifications": [ "Classlib", "Console", "XUnit" ],
  "identity": "Lucabol.SingleSourceProject",
  "name": "One single Project",
  "description": "One single Project for DLL, XUnit, Benchmark & Main, using configurations to decide what to compile",
  "shortName": "oneproject",
  "tags": {
    "language": "C#",
    "type": "project"
  "preferNameDirectory": true,
  "sourceName": "SingleSourceProject",
    "standardVersion": {
      "type": "parameter",
      "defaultValue": "netstandard2.0",
    "appVersion": {
      "type": "parameter",
      "defaultValue": "netcoreapp2.1",


Now that you know how it all works, you can make an informed decision if to use it or not. As for me …

comments powered by Disqus Updated: 2019-03-14 13:54:40 +0100 +0100, Version: a26e011