test helper tests: use stubs instead of spys for buster's fail and log functions, make it harder to forget restoring them
add done(shouldNotProduceError) where there's no error callback at all
replace error callback `done` by `done(shouldProduceError)`
replace "noop" as non-error callback by `done(shouldProduceError)`
replace literal empty function as non-error callback by `done(shouldProduceError)`
replace literal `...assert(false, "should produce error")...` as non-error callback by `done(shouldProduceError)`
replace just `done` as non-error callback by `done(shouldProduceError)`