Azure DevOps pipeline DotNetCore test path projects pattern

Question

I want to test my .NET Core 5.0 projects in the Azure DevOps pipeline. When using a full path to one of my test projects the pipeline will test that single project. When using a pattern to search for all my test projects he can't find one of them.

My project structure is as follows:

1. backend
   1. DemoProject (with the .sln file)
      1. DemoProject.Application
      2. DemoProject.Application.Test
      3. DemoProject.Persistence
      4. DemoProject.Persistence.Test
   2. DemoProject 2
      1. ....

 I created a simple version of my pipeline template:

- master

pool:
  vmImage: ubuntu-latest

steps:
- task: DotNetCoreCLI@2
  inputs:
    command: 'test'
    projects: './backend/DemoProject/DemoProject.Application.Tests/DemoProject.Application.Tests.csproj'

When using the full path (./backend/DemoProject/DemoProject.Application.Tests/DemoProject.Application.Tests.csproj), the pipeline find's the selected project. When using a pattern. (./backend/DemoProject/\*\*/\*.Tests.csproj or ./backend/DemoProject/\*\*/DemoProject.Application.Tests.csproj), the pipeline can't find any project.

Does someone know what the correct pattern is to run all my test projects inside the DemoProject folder?