Tidy `t/coverage/set-immediate.t.js`.

See #351.
Tidy `t/coverage/split-race.t.js`.

See #351.
Use `assert` in `t/coverage/split-race.t.js`.

See #351.
Use `vivify` in `t/coverage/split-race.t.js`.

See #352.
Tidy `t/coverage/upgrade.t.js`.

See #351.
Tidy `t/coverage/validator.t.js`.

See #351.
Use `assert` in `t/coverage/validator.t.js`.

See #351.
Tidy `t/coverage/write.t.js`.

See #351.
Use `assert` in `t/coverage/write.t.js`.

See #351.
Use `vivify` in `t/coverage/write.t.js`.

See #351.
Tidy `t/delete/ghost.t.js`.

See #351.
Tidy `t/ghost/empty.t.js`.

See #351.
Use `assert` in `t/delete/ghost.t.js`.

See #351.
Use `vivify` in `t/delete/ghost.t.js`.

See #351.
Use `assert` in `t/ghost/empty.t.js`.

See #351.
Use `vivify` in `t/ghost/empty.t.js`.

See #351.
Tidy `t/delete/exorcise.t.js`.

See #351.
Use `assert` in `t/ghost/exorcise.t.js`.

See #351.
Use `vivify` in `t/ghost/exorcise.t.js`.

See #352.
Tidy `t/ghost/first.t.js`.

See #351.