Fix get_collections and conformance checking behavior

[duckontheweb]

Related Issue(s):

None

Description:

The Client.get_collections docs state that it will fallback to the pystac.Catalog behavior of following "child" links if the API landing page does not include the proper conformance class for the /collections endpoint. The actual behavior when running this against an API that lacks the conformance class is that a NotImplementedError is raised:

>>> from pystac_client import Client
>>> client = Client.open("http://api.radiant.earth/mlhub/v1")
>>> next(client.get_collections())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/jduckworth/Code/stac/pystac-client/pystac_client/client.py", line 97, in get_collections
    if self._stac_io.assert_conforms_to(ConformanceClasses.COLLECTIONS):
  File "/Users/jduckworth/Code/stac/pystac-client/pystac_client/stac_api_io.py", line 225, in assert_conforms_to
    raise NotImplementedError(f"{conformance_class} not supported")
NotImplementedError: ConformanceClasses.COLLECTIONS not supported

The root cause was that StacApiIO.assert_conforms_to was being used in if statements that expected a boolean response when in fact it returned True if the API conformed and raised the above exception if it did not. Having this kind of mixed response seemed like a confusing pattern, so I changed that method to raise the exception when conformance fails and not have any return value. Code that expects a boolean response now exclusively uses the StacApiIO.conforms_to method.

PR Checklist:

• Code is formatted
• Tests pass
• Changes are added to the CHANGELOG

[codecov-commenter]

Codecov Report

Merging #120 (92c2abd) into main (9e010ad) will increase coverage by 1.24%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     #120      +/-   ##
==========================================
+ Coverage   78.71%   79.96%   +1.24%     
==========================================
  Files           9        9              
  Lines         545      544       -1     
==========================================
+ Hits          429      435       +6     
+ Misses        116      109       -7     

Impacted Files	Coverage Δ
pystac_client/client.py	81.81% <33.33%> (+1.81%)	⬆️
pystac_client/stac_api_io.py	82.07% <100.00%> (+5.43%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9e010ad...92c2abd. Read the comment docs.

[gadomski]

NBD but this will conflict with #118 (maybe auto-deconflictable?).

[duckontheweb]

Yeah, I'm not sure if git will just resolve it automatically since it's the same change in the same place, but either way it should be easy to resolve. I can rebase one of these PRs once the other has been merged if it helps.

[matthewhanson]

This all makes sense to me WRT the behavior of the asset function. Thanks for the PR and big thanks for the additional tests