Consider the following transcript:

    $ make maintainer-clean
    $ cabal test
    [...]
    ^C to interrupt cabal test
    $ cabal clean
    cleaning...
    $ ls -1d tests*/
    tests/
    tests-darcs-2.dir/
    tests-hashed.dir/

The last two lines indicate intermediary directories created by "cabal
test" but not removed by "cabal clean".

PS: solutions to this may be affected by issue1283.

The following patch updated the status of issue1285 to be resolved:

* Resolve issue1285: remove "cabal test" intermediaries.