Added ValueError test for Epsilon class and comments about raising Va…

…lueError.

moe/bandit/epsilon.py

@@ -54,10 +54,11 @@ def get_winning_arm_names(arms_sampled):
         :type arms_sampled: dictionary of (String(), SampleArm()) pairs
         :return: of set of names of the winning arms
         :rtype: frozenset(String())
+        :raise: ValueError when ``arms_sampled`` are empty.
 
         """
         if not arms_sampled:
-            raise ValueError('sample_arms is empty!')
+            raise ValueError('arms_sampled is empty!')
 
         avg_payoff_arm_name_list = []
         for arm_name, sampled_arm in arms_sampled.iteritems():

moe/bandit/epsilon_first.py

@@ -85,6 +85,7 @@ def allocate_arms(self):
 
         :return: the dictionary of (arm, allocation) key-value pairs
         :rtype: a dictionary of (String(), float64) pairs
+        :raise: ValueError when ``sample_arms`` are empty.
 
         """
         arms_sampled = self._historical_info.arms_sampled

moe/bandit/epsilon_greedy.py

@@ -60,6 +60,7 @@ def allocate_arms(self):
 
         :return: the dictionary of (arm, allocation) key-value pairs
         :rtype: a dictionary of (String(), float64) pairs
+        :raise: ValueError when ``sample_arms`` are empty.
 
         """
         arms_sampled = self._historical_info.arms_sampled

moe/tests/bandit/epsilon_test.py

@@ -4,6 +4,8 @@
 Test functions in :class:`moe.bandit.epsilon.Epsilon`
 
 """
+import logging
+
 import testify as T
 
 from moe.bandit.epsilon import Epsilon
@@ -14,6 +16,20 @@ class EpsilonTest(EpsilonTestCase):
 
     """Verify that different sample_arms return correct results."""
 
+    @T.class_setup
+    def disable_logging(self):
+        """Disable logging (for the duration of this test case)."""
+        logging.disable(logging.CRITICAL)
+
+    @T.class_teardown
+    def enable_logging(self):
+        """Re-enable logging (so other test cases are unaffected)."""
+        logging.disable(logging.NOTSET)
+
+    def test_empty_arm_invalid(self):
+        """Test empty ``sample_arms`` causes an ValueError."""
+        T.assert_raises(ValueError, Epsilon.get_winning_arm_names, {})
+
     def test_two_new_arms(self):
         """Check that the two-new-arms case always returns both arms as winning arms. This tests num_winning_arms == num_arms > 1."""
         T.assert_sets_equal(Epsilon.get_winning_arm_names(self.two_new_arms_test_case.arms_sampled), frozenset(["arm1", "arm2"]))