-test_expect_success \
- "--format=mbox --part=1, incompatible, expect error" \
- "! notmuch show --format=mbox --part=1 'id:87liy5ap00.fsf@yoom.home.cworth.org'"
+test_begin_subtest "--format=mbox --part=1, incompatible, expect error"
+test_expect_success "! notmuch show --format=mbox --part=1 'id:87liy5ap00.fsf@yoom.home.cworth.org'"