Fix and modify unit test re #8705

This fix has removed the capability to handle a non-grouped workspace,
but this capability is not needed.
The change prepares the code for #8402 .

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>
Update documentation and tidy up re #8705

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>
Merge remote-tracking branch 'origin/feature/8705_one_table'