Sanity tests:
PASS: [1s linear] iteration time was [null] at -1s
PASS: [1s linear] iteration time was [0] at 0s
PASS: [1s linear] iteration time was [0.5] at 0.5s
PASS: [1s linear] iteration time was [0.2] at 0.2s
PASS: [1s linear] iteration time was [0.8] at 0.8s
PASS: [1s linear] iteration time was [null] at 2s

Fill-mode:
PASS: [1s none] iteration time was [null] at -1s
PASS: [1s none] iteration time was [null] at 2s
PASS: [1s both] iteration time was [0] at -1s
PASS: [1s both] iteration time was [1] at 2s
PASS: [1s forwards] iteration time was [null] at -1s
PASS: [1s forwards] iteration time was [1] at 2s
PASS: [1s backwards] iteration time was [0] at -1s
PASS: [1s backwards] iteration time was [null] at 2s

Fill-mode + reverse direction:
PASS: [1s none reverse] iteration time was [null] at -1s
PASS: [1s none reverse] iteration time was [null] at 2s
PASS: [1s both reverse] iteration time was [1] at -1s
PASS: [1s both reverse] iteration time was [0] at 2s
PASS: [1s forwards reverse] iteration time was [null] at -1s
PASS: [1s forwards reverse] iteration time was [0] at 2s
PASS: [1s backwards reverse] iteration time was [1] at -1s
PASS: [1s backwards reverse] iteration time was [null] at 2s

End exclusive timing:
PASS: [1s] iteration time was [null] at 1s

Zero duration:
PASS: [none] iteration time was [null] at -1s
PASS: [none] iteration time was [null] at 0s
PASS: [none] iteration time was [null] at 1s
PASS: [both] iteration time was [0] at -1s
PASS: [both] iteration time was [1] at 0s
PASS: [both] iteration time was [1] at 1s
PASS: [forwards] iteration time was [null] at -1s
PASS: [forwards] iteration time was [1] at 0s
PASS: [forwards] iteration time was [1] at 1s
PASS: [backwards] iteration time was [0] at -1s
PASS: [backwards] iteration time was [null] at 0s
PASS: [backwards] iteration time was [null] at 1s

Zero duration + reverse direction:
PASS: [none reverse] iteration time was [null] at -1s
PASS: [none reverse] iteration time was [null] at 0s
PASS: [none reverse] iteration time was [null] at 1s
PASS: [both reverse] iteration time was [1] at -1s
PASS: [both reverse] iteration time was [0] at 0s
PASS: [both reverse] iteration time was [0] at 1s
PASS: [forwards reverse] iteration time was [null] at -1s
PASS: [forwards reverse] iteration time was [0] at 0s
PASS: [forwards reverse] iteration time was [0] at 1s
PASS: [backwards reverse] iteration time was [1] at -1s
PASS: [backwards reverse] iteration time was [null] at 0s
PASS: [backwards reverse] iteration time was [null] at 1s

Zero iterations:
PASS: [1s 0s 0 none] iteration time was [null] at -1s
PASS: [1s 0s 0 none] iteration time was [null] at 0s
PASS: [1s 0s 0 none] iteration time was [null] at 0.5s
PASS: [1s 0s 0 none] iteration time was [null] at 2s
PASS: [1s 0s 0 both] iteration time was [0] at -1s
PASS: [1s 0s 0 both] iteration time was [0] at 0s
PASS: [1s 0s 0 both] iteration time was [0] at 2s
PASS: [1s 0s 0 forwards] iteration time was [null] at -1s
PASS: [1s 0s 0 forwards] iteration time was [0] at 0s
PASS: [1s 0s 0 forwards] iteration time was [0] at 2s
PASS: [1s 0s 0 backwards] iteration time was [0] at -1s
PASS: [1s 0s 0 backwards] iteration time was [null] at 0s
PASS: [1s 0s 0 backwards] iteration time was [null] at 2s

Zero iterations, zero duration:
PASS: [0s 0s 0 none] iteration time was [null] at -1s
PASS: [0s 0s 0 none] iteration time was [null] at 0s
PASS: [0s 0s 0 none] iteration time was [null] at 2s
PASS: [0s 0s 0 both] iteration time was [0] at -1s
PASS: [0s 0s 0 both] iteration time was [0] at 0s
PASS: [0s 0s 0 both] iteration time was [0] at 1s
PASS: [0s 0s 0 forwards] iteration time was [null] at -1s
PASS: [0s 0s 0 forwards] iteration time was [0] at 0s
PASS: [0s 0s 0 forwards] iteration time was [0] at 1s
PASS: [0s 0s 0 backwards] iteration time was [0] at -1s
PASS: [0s 0s 0 backwards] iteration time was [null] at 0s
PASS: [0s 0s 0 backwards] iteration time was [null] at 1s

Multiple iterations:
PASS: [1s 2 linear] iteration time was [null] at -1s
PASS: [1s 2 linear] iteration time was [0] at 0s
PASS: [1s 2 linear] iteration time was [0.4] at 0.4s
PASS: [1s 2 linear] iteration time was [0] at 1s
PASS: [1s 2 linear] iteration time was [0.6] at 1.6s
PASS: [1s 2 linear] iteration time was [null] at 2s
PASS: [1s 2 linear reverse] iteration time was [1] at 0s
PASS: [1s 2 linear reverse] iteration time was [0.6] at 0.4s
PASS: [1s 2 linear reverse] iteration time was [1] at 1s
PASS: [1s 2 linear reverse] iteration time was [0.4] at 1.6s
PASS: [1s 2 linear alternate] iteration time was [0] at 0s
PASS: [1s 2 linear alternate] iteration time was [0.4] at 0.4s
PASS: [1s 2 linear alternate] iteration time was [1] at 1s
PASS: [1s 2 linear alternate] iteration time was [0.4] at 1.6s
PASS: [1s 2 linear alternate-reverse] iteration time was [1] at 0s
PASS: [1s 2 linear alternate-reverse] iteration time was [0.6] at 0.4s
PASS: [1s 2 linear alternate-reverse] iteration time was [0] at 1s
PASS: [1s 2 linear alternate-reverse] iteration time was [0.6] at 1.6s

Fractional iterations:
PASS: [1s 0.5 linear] iteration time was [null] at -1s
PASS: [1s 0.5 linear] iteration time was [0] at 0s
PASS: [1s 0.5 linear] iteration time was [0.2] at 0.2s
PASS: [1s 0.5 linear] iteration time was [null] at 0.5s
PASS: [1s 1.5 linear] iteration time was [null] at -1s
PASS: [1s 1.5 linear] iteration time was [0] at 0s
PASS: [1s 1.5 linear] iteration time was [0.5] at 0.5s
PASS: [1s 1.5 linear] iteration time was [0] at 1s
PASS: [1s 1.5 linear] iteration time was [0.4] at 1.4s
PASS: [1s 1.5 linear] iteration time was [null] at 1.5s
PASS: [1s 1.5 linear reverse] iteration time was [null] at -1s
PASS: [1s 1.5 linear reverse] iteration time was [1] at 0s
PASS: [1s 1.5 linear reverse] iteration time was [0.5] at 0.5s
PASS: [1s 1.5 linear reverse] iteration time was [1] at 1s
PASS: [1s 1.5 linear reverse] iteration time was [0.6] at 1.4s
PASS: [1s 1.5 linear reverse] iteration time was [null] at 1.5s
PASS: [1s 1.6 linear forwards] iteration time was [0.6] at 2s
PASS: [1s 1.6 linear forwards reverse ] iteration time was [0.4] at 2s
PASS: [1s 0.6 linear backwards reverse] iteration time was [1] at -1s

Infinite iterations:
PASS: [1s infinite linear] iteration time was [0] at 1s
PASS: [1s infinite linear] iteration time was [0] at 10s
PASS: [1s infinite linear] iteration time was [0] at 1000s
PASS: [1s infinite linear] iteration time was [0.4] at 1000.4s

Infinite iterations, zero duration:
PASS: [0s infinite linear] iteration time was [null] at -1s
PASS: [0s infinite linear] iteration time was [null] at 0s
PASS: [0s infinite linear] iteration time was [null] at 2s