doc: clarify get_test_params return type and validate parameter_set

Address review feedback: document list return type, reject unknown
parameter_set values with a clear error.

Author: AbinaShah

pyaptamer/trafos/encode/_greedy.py

@@ -136,11 +136,21 @@ def _transform(self, X):
     def get_test_params(cls, parameter_set="default"):
         """Get test parameters for GreedyEncoder.
 
+        Parameters
+        ----------
+        parameter_set : str, default="default"
+            Name of the parameter set to return. Only ``"default"`` is supported.
+
         Returns
         -------
-        params : dict
-            Test parameters for GreedyEncoder.
+        list[dict]
+            List of parameter dictionaries for constructing test instances.
         """
+        if parameter_set != "default":
+            raise ValueError(
+                'parameter_set must be "default"; '
+                f"got {parameter_set!r}"
+            )
         param0 = {
             "words": {"A": 1, "C": 2, "G": 3, "U": 4, "AC": 5, "GU": 6},
         }

pyaptamer/trafos/encode/tests/test_greedy_encoder.py

@@ -1,6 +1,7 @@
 import inspect
 
 import pandas as pd
+import pytest
 
 from pyaptamer.trafos.encode import GreedyEncoder
 
@@ -9,12 +10,19 @@ def test_get_test_params_is_classmethod_and_callable():
     descriptor = inspect.getattr_static(GreedyEncoder, "get_test_params")
     assert isinstance(descriptor, classmethod)
 
+    params_default = GreedyEncoder.get_test_params(parameter_set="default")
     params = GreedyEncoder.get_test_params()
+    assert params == params_default
     assert isinstance(params, list)
     assert len(params) >= 1
     assert all(isinstance(p, dict) for p in params)
 
 
+def test_get_test_params_unknown_parameter_set_raises():
+    with pytest.raises(ValueError, match='parameter_set must be "default"'):
+        GreedyEncoder.get_test_params(parameter_set="not_a_real_set")
+
+
 def test_greedy_encoder_can_construct_from_test_params():
     for params in GreedyEncoder.get_test_params():
         enc = GreedyEncoder(**params)