Tests needed:

   - Fail if cache_dir from previous run cannot be deleted
   - Fail if cache_dir cannot be created from current out_dir
   - transfer_type_explorers: Explorers are not transferred twice
   - transfer_type_explorers: No transfer tried if there are no type_explorers

   - does $require work?
   - $whatever should fail if there is no global explorer directory
   - emulator may only be called with __ as prefix - fail otherwise!

   - ensure paths returned by object include dot-cdist
   - ensure path of explorer of object returns correct path

   config_install:
      run_type_manifest() - same tests as for test_initial_manifest_*?
      run_manifest() - raise exception if manifest is not existent
      object_run(): ensure no object is run twice
      object_run(): ensure requirements are taken into account
      object_run(): check (from extern?) that all needed variables are setup
      object_run(): ensure no code-{local, remote} is created, if gencode is not producing code
      object_run(): ensure no code-{local, remote} contains what gencode created

      run_type_explorer(): ensure output is saved to correct path
      run_type_explorer(): ensure a type with no explorers works
      run_type_explorer(): ensure environment is setup correctly


      all: check that messages of all functions contain target_host in string