Add a test for basic sklearn API conformance

The "default constructible" (i.e. no required __init__ parameters)
property is the most basic property of a scikit-learn estimator. It is a
prerequisite for all other estimator checks.

csrank/tests/test_estimators.py

@@ -0,0 +1,75 @@
+"""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_parameters_default_constructible
+
+from csrank.choicefunction import CmpNetChoiceFunction
+from csrank.choicefunction import FATEChoiceFunction
+from csrank.choicefunction import FATELinearChoiceFunction
+from csrank.choicefunction import FETAChoiceFunction
+from csrank.choicefunction import FETALinearChoiceFunction
+from csrank.choicefunction import GeneralizedLinearModel
+from csrank.choicefunction import PairwiseSVMChoiceFunction
+from csrank.choicefunction import RankNetChoiceFunction
+from csrank.discretechoice import CmpNetDiscreteChoiceFunction
+from csrank.discretechoice import FATEDiscreteChoiceFunction
+from csrank.discretechoice import FATELinearDiscreteChoiceFunction
+from csrank.discretechoice import FETADiscreteChoiceFunction
+from csrank.discretechoice import FETALinearDiscreteChoiceFunction
+from csrank.discretechoice import GeneralizedNestedLogitModel
+from csrank.discretechoice import MixedLogitModel
+from csrank.discretechoice import MultinomialLogitModel
+from csrank.discretechoice import NestedLogitModel
+from csrank.discretechoice import PairedCombinatorialLogit
+from csrank.discretechoice import PairwiseSVMDiscreteChoiceFunction
+from csrank.discretechoice import RankNetDiscreteChoiceFunction
+from csrank.objectranking import CmpNet
+from csrank.objectranking import ExpectedRankRegression
+from csrank.objectranking import FATELinearObjectRanker
+from csrank.objectranking import FATEObjectRanker
+from csrank.objectranking import FETALinearObjectRanker
+from csrank.objectranking import FETAObjectRanker
+from csrank.objectranking import ListNet
+from csrank.objectranking import RankNet
+from csrank.objectranking import RankSVM
+
+
+@pytest.mark.parametrize(
+    "Estimator",
+    [
+        CmpNet,
+        CmpNetChoiceFunction,
+        CmpNetDiscreteChoiceFunction,
+        ExpectedRankRegression,
+        FATEChoiceFunction,
+        FATEDiscreteChoiceFunction,
+        FATELinearChoiceFunction,
+        FATELinearDiscreteChoiceFunction,
+        FATELinearObjectRanker,
+        FATEObjectRanker,
+        FETAChoiceFunction,
+        FETADiscreteChoiceFunction,
+        FETALinearChoiceFunction,
+        FETALinearDiscreteChoiceFunction,
+        FETALinearObjectRanker,
+        FETAObjectRanker,
+        GeneralizedLinearModel,
+        GeneralizedNestedLogitModel,
+        ListNet,
+        MixedLogitModel,
+        MultinomialLogitModel,
+        NestedLogitModel,
+        PairedCombinatorialLogit,
+        PairwiseSVMChoiceFunction,
+        PairwiseSVMDiscreteChoiceFunction,
+        RankNet,
+        RankNetChoiceFunction,
+        RankNetDiscreteChoiceFunction,
+        RankSVM,
+    ],
+)
+def test_all_estimators(Estimator):
+    check_parameters_default_constructible("default_constructible", Estimator)