Fix padding issue on axis tick labels

To clarify, there is no `isVertical` function, so we need only two tests.

I think that these tests are out of place, because we are really testing the effect of `chart.xAxis(axis)` and `chart.yAxis(axis)` on `axis.isHorizontal()`.

I propose that I split the tests in two.

- One set of tests checking chart updates axis internal state `direction`.
- Another test to check axis external state gives correct result with `isHorizontal`.

Should be a quick change.