First pass of tests

Author: jpolchlo

pystac/extensions/classification.py

@@ -168,6 +168,12 @@ def apply(
         self.description = description
         self.name = name
 
+        assert offset >= 0, "Non-negative offsets only"
+        assert length >= 1, "Positive field lengths only"
+
+        class_coverage = set([c.value for c in classes])
+        assert set(range(0, 2**length)) - class_coverage == set(), "Classes must cover the complete range of values"
+
     @classmethod
     def create(
         cls,