WIP: Test estimator API

This isn't ready yet. It currently fails because we don't provide a
get_params function.

csrank/tests/test_estimators.py

@@ -0,0 +1,23 @@
+"""Check that our estimators adhere to the scikit-learn interface.
+
+https://scikit-learn.org/stable/developers/develop.html#rolling-your-own-estimator
+"""
+
+import pytest
+from sklearn.utils.estimator_checks import check_estimator
+
+from csrank.choicefunction import FETALinearChoiceFunction
+from csrank.discretechoice import FETALinearDiscreteChoiceFunction
+from csrank.objectranking import FETALinearObjectRanker
+
+
+@pytest.mark.parametrize(
+    "Estimator",
+    [
+        FETALinearChoiceFunction,
+        FETALinearDiscreteChoiceFunction,
+        FETALinearObjectRanker,
+    ],
+)
+def test_all_estimators(Estimator):
+    return check_estimator(Estimator)