This harness function is not necessary in the majority of cases in which
it is used. Remove its usage to simplify tests and decrease the amount
of domain-specific knowledge necessary to contribute to the test suite.
Persist the harness function itself for use by future tests for ES2015
modules (such a helper is necessary for tests that are interpreted as
module code).
For asynchronous tests, the contract between test file and test runner
is implicit: runners are expected to inspect the source code for
references to a global `$DONE` identifier.
Promote a more explicit contract between test file and test runner by
introducing a new frontmatter "tag", `async`. This brings asynchronous
test configuration in-line with other configuration mechanisms and also
provides a more natural means of test filtering.
The modifications to test files was made programatically using the
`grep` and `sed` utilities:
$ grep "\$DONE" test/ -r --files-with-match --null | \
xargs -0 sed -i 's/^\(flags:\s*\)\[/\1[async, /g'
$ grep "\$DONE" test/ -rl --null | \
xargs -0 grep -E '^flags:' --files-without-match --null | \
xargs -0 sed -i 's/^---\*\//flags: [async]\n---*\//'
