Move tests to separate folder

tests/problems/test_knapsack.py

@@ -0,0 +1,24 @@
+#  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.
+
+import numpy as np
+from scipy.stats import uniform, randint
+
+from miplearn.problems.knapsack import MultiKnapsackGenerator
+
+
+def test_knapsack_generator():
+    gen = MultiKnapsackGenerator(
+        n=randint(low=100, high=101),
+        m=randint(low=30, high=31),
+        w=randint(low=0, high=1000),
+        K=randint(low=500, high=501),
+        u=uniform(loc=1.0, scale=1.0),
+        alpha=uniform(loc=0.50, scale=0.0),
+    )
+    instances = gen.generate(100)
+    w_sum = sum(instance.weights for instance in instances) / len(instances)
+    b_sum = sum(instance.capacities for instance in instances) / len(instances)
+    assert round(np.mean(w_sum), -1) == 500.0
+    assert round(np.mean(b_sum), -3) == 25000.0