add tests for property filters

[bossie]

Part of #460.

[bossie]

@soxofaan,

I'm trying to address this TODO here but can't seem to find the way to implement it:

openeo-geopyspark-driver/tests/test_api_result.py

Lines 4006 to 4007 in 66da616

	# TODO: check if only items that match this property are included,
	# e.g. with calls to org.openeo.opensearch.OpenSearchResponses.featureBuilder().withId("item01")

What the test does is pass a property filter ("season" == "s1") to load_stac so only STAC Item "item01" is loaded ("item02" doesn't have this "season" property).

To this end, I'm trying to see if (in pseudocode) org.openeo.geotrellis.file.FixedFeaturesOpenSearchClient().addFeature() is called exactly once with Feature("item01"):

openeo-geopyspark-driver/openeogeotrellis/load_stac.py

Line 324 in 66da616

opensearch_client.addFeature(f)

Some guidance?