add test for BalancingLearner edge case

Author: jhoofwijk

adaptive/tests/test_balancing_learner.py

@@ -0,0 +1,23 @@
+# -*- coding: utf-8 -*-
+
+from ..learner import Learner1D, BalancingLearner
+
+
+def test_balancing_learner_loss_cache():
+    learner = Learner1D(lambda x: x, bounds=(-1, 1))
+    learner.tell(-1, -1)
+    learner.tell(1, 1)
+    learner.tell_pending(0)
+
+    real_loss = learner.loss(real=True)
+    pending_loss = learner.loss(real=False)
+
+    # Test if the real and pending loss are cached correctly
+    bl = BalancingLearner([learner])
+    assert bl.loss(real=True) == real_loss
+    assert bl.loss(real=False) == pending_loss
+
+    # Test if everything is still fine when executed in the reverse order
+    bl = BalancingLearner([learner])
+    assert bl.loss(real=False) == pending_loss
+    assert bl.loss(real=True) == real_loss