TEST: check that command does not fail with stackrtace
TMP LOCAL: mark as TODO so far
TEST: close input, to prevent (infinite) retrying in case of parsing false
IMPL: verify marks after editing TODO
DOC: add TODO about handling refs in merges
FIXUP: array dereference
FIX: exit status in case of invalid TODO
TEST: no TODO anymore
gh-21: verify marks after todo editing

Check that all marks are defined before use, suggest to reedit if they
are not. Also things discovered during testing are fixed
gh-7: verify in itest that stack trace is never printer by testee