coordinate testing

[mpu-creare]

This involves migrating some old unit tests to pytests, writing some new unit tests, and removing some old unit tests.

• util
• base_coordinates
• coordinates1d
• array_coordinates1d
• uniform_coordinates1d
• stacked_coordinates
• coordinates
• cfunctions
• group coordinates

[jmilloy]

@mpu-creare Are NaN values allowed in Coord or MonotonicCoord? I would assume definitely not in MonotonicCoord...?

[mpu-creare]

NaN's should not be allowed in coordinates... until we have a use-case that requires it.

I have had cases where my input sources put NaNs in their coordinates, but there I have to fix up their coordinates anyway... so perhaps we need tools to fill NaNs... but those already exist in xarray.

[jmilloy]

@mpu can the padding for a coord select or intersect be negative?

[mpu-creare]

No.

[jmilloy]

This issue should now be addressed again in earnest alongside #84.

[jmilloy]

I still need to test the intersect method in Coordinates, StackedCoordinates, and GroupCoordinates. But we've reached >90% for the coordinates, so I'm to close this. I'll need to add tests for select when I implement #118 so I will add intersect tests then, too.