This tests that tick marks don't break when the axis crosses into daylight savings time.
The tick marks should all be on day boundaries or nice hours (6, 12, 18), rather than on odd time boundaries like 5, 11, 17 and 23.
This chart shows a continuous line going across the "fall back" EST/EDT event. You may need to switch your computer's time zone to Eastern to see this. The x-axis tick marks go from 01:00 → 01:55 and then back to 01:00.