AdaptiveClassifier: Refactor and add tests

tests/classifiers/__init__.py

@@ -1,3 +1,39 @@
 #  MIPLearn: Extensible Framework for Learning-Enhanced Mixed-Integer Optimization
 #  Copyright (C) 2020, UChicago Argonne, LLC. All rights reserved.
 #  Released under the modified BSD license. See COPYING.md for more details.
+
+from typing import Tuple
+
+import numpy as np
+from sklearn.preprocessing import StandardScaler
+
+
+def _build_circle_training_data() -> Tuple[np.ndarray, np.ndarray]:
+    x_train = StandardScaler().fit_transform(
+        np.array(
+            [
+                [
+                    x1,
+                    x2,
+                ]
+                for x1 in range(-10, 11)
+                for x2 in range(-10, 11)
+            ]
+        )
+    )
+    y_train = np.array(
+        [
+            [
+                False,
+                True,
+            ]
+            if x1 * x1 + x2 * x2 <= 100
+            else [
+                True,
+                False,
+            ]
+            for x1 in range(-10, 11)
+            for x2 in range(-10, 11)
+        ]
+    )
+    return x_train, y_train