Ensure behavior DSCIM depends on is covered by good unit tests

[brews]

dscim is a downstream dependency of this package. This package has some spotty test coverage in places. It would be great is we could double check, and if need be, write in unit or integration tests to cover the behavior that dscim depends on.

[brews]

@kemccusker could I get your help and have you take this or collaborate and help look at this problem on the dscim end of things. I'd like to ensure we have good enough tests to not accidentally break something dscim depends on.

[brews]

In dscim v0.4.0 is looks like this weighted_quantile_xr() function gets called. We'll want to ensure it gets tested, especially when the input data is a xr.Dataset. On quick look through the coverage information we have online, it doesn't look like that's the case.

I also haven't looked to see what existing tests run the function for or if they're even checking it's behavior.