Outsourcing the test files into separate folder

[Nano1237]

Is your feature request related to a problem? Please describe.
The folder structure is currently not scalable. For each new feature, a test file is placed in the same folder, which doubles the size of the folder and the clarity is lost.

Describe the solution you'd like
Die Ordnersturktur könnte in zukunft z.B. so aussehen:

• .github
• src
  • ...
• test(s)
  • unit
    • ...
  • bdd
    • ...