Use constants to describe purpose and importance of test data

CONSTANTS some_nonsense_key TYPE char8 VALUE 'ABCDEFGH'.

METHOD throws_on_invalid_entry.
  TRY.
      " when
      cut->read_entry( some_nonsense_key ).
      cl_abap_unit_assert=>fail( ).
    CATCH /clean/customizing_reader_error.
      " then
  ENDTRY.
ENDMETHOD.