Unit testing code from a separate project

The other day I answered a question on StackOverflow on how to unit test code from a separate project. To increase its exposure I also added it here.

• Code

Say you have a TwinCAT project called MyProject which you want to test with the TcUnit library. For this you create another project MyProject_Tests. So you have the following folder structure:

repos
  ├── MyProject
  |  ├── MyProject
  |  |  ├── Plc
  |  |  |  ├── POUs
  |  |  |  └── Plc.plcproj
  |  |  └── MyProject.tsproj
  |  └── MyProject.sln
  |
  ├── MyProject_Tests
  |  ├── MyProject_Tests
  |  |  ├── Plc
  |  |  |  ├── POUs
  |  |  |  └── Plc.plcproj
  |  |  └── MyProject_Tests.tsproj
  |  └── MyProject_Tests.sln
  |
  └── hardlinkPousToTestProject.bat

You then:

1. Add a folder Tests under Plc in the MyProject_Tests project.
2. Add a method you want to test to MyProject/MyProject/Plc/POUs.
3. Edit the path names in hardlinkPousToTestProject.bat such that they point to the correct folders. So for the current example:
   • for %%i in (.\path\to\project\POUs\*.TcPOU) do ( becomes for %%i in (.\MyProject\MyProject\Plc\POUs\*.TcPOU) do (
   • and mklink /H .\path\to\testproject\POUs\%%~nxi %%i becomes mklink /H .\MyProject_Tests\MyProject_Tests\Plc\POUs\%%~nxi %%i
4. Run the batch script.
5. Manually add the .TcPOU files to the _MyProject\_Tests_ project
6. Add the MyProject_Tests\MyProject_Tests\Plc\POUs folder to the .gitignore file since these files are already in MyProject.

Your file structure should now look like this:

repos
  ├── MyProject
  |  ├── MyProject
  |  |  ├── Plc
  |  |  |  ├── POUs
  |  |  |  |  └── Function.TcPOU  # Original file
  |  |  |  └── Plc.plcproj
  |  |  └── MyProject.tsproj
  |  └── MyProject.sln
  |
  ├── MyProject_Tests
  |  ├── MyProject_Tests
  |  |  ├── Plc
  |  |  |  ├── POUs
  |  |  |  |  └── Function.TcPOU   # Hard linked file
  |  |  |  ├── Tests
  |  |  |  |  └── Function_Tests.TcPOU
  |  |  |  └── Plc.plcproj
  |  |  └── MyProject_Tests.tsproj
  |  └── MyProject_Tests.sln
  |
  └── hardlinkPousToTestProject.bat

Now you can change Function.TcPOU from either MyProject or MyProject_Tests!

What is hard linking?

With hard linking, identical copies of a file are created. All the copies still point to the original file. So, whenever a change is made to a hard linked file, or the original, the changes show up in all the files. Hard linking basically creates multiple access points to the same file from different locations.

Discuss: Github snippet.