running 4 tests
test add  ... bench:           1.24 ns/iter (+/- 0.00)
test add2 ... bench:           1.48 ns/iter (+/- 0.01)
test add3 ... bench:           1.72 ns/iter (+/- 0.01)
test add4 ... bench:           1.96 ns/iter (+/- 0.01)
test empty ... bench:           1.24 ns/iter (+/- 0.00)