Move statistical functions in bisect script to their own module.

tools/auto_bisect/math_utils_test.py

+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import math
+import unittest
+
+import math_utils
+
+
+class MathUtilsTest(unittest.TestCase):
+  """Tests for mathematical utility functions."""
+
+  def testTruncatedMeanRaisesError(self):
+    """TruncatedMean should raise an error when passed an empty list."""
+    with self.assertRaises(TypeError):
+      math_utils.TruncatedMean([], 0)
+
+  def testMeanSingleNum(self):
+    """Tests the Mean function with a single number."""
+    self.assertEqual(3.0, math_utils.Mean([3]))
+
+  def testMeanShortList(self):
+    """Tests the Mean function with a short list."""
+    self.assertEqual(0.5, math_utils.Mean([-3, 0, 1, 4]))
+
+  def testMeanCompareAlternateImplementation(self):
+    """Tests Mean by comparing against an alternate implementation."""
+    def AlternateMeanFunction(values):
+      """Simple arithmetic mean function."""
+      return sum(values) / float(len(values))
+    test_values_lists = [[1], [5, 6.5, 1.2, 3], [-3, 0, 1, 4],
+                         [-3, -1, 0.12, 0.752, 3.33, 8, 16, 32, 439]]
+    for values in test_values_lists:
+      self.assertEqual(
+          AlternateMeanFunction(values),
+          math_utils.Mean(values))
+
+  def testRelativeChange(self):
+    """Tests the common cases for calculating relative change."""
+    # The change is relative to the first value, regardless of which is bigger.
+    self.assertEqual(0.5, math_utils.RelativeChange(1.0, 1.5))
+    self.assertEqual(0.5, math_utils.RelativeChange(2.0, 1.0))
+
+  def testRelativeChangeFromZero(self):
+    """Tests what happens when relative change from zero is calculated."""
+    # If the first number is zero, then the result is not a number.
+    self.assertEqual(0, math_utils.RelativeChange(0, 0))
+    self.assertTrue(
+        math.isnan(math_utils.RelativeChange(0, 1)))
+    self.assertTrue(
+        math.isnan(math_utils.RelativeChange(0, -1)))
+
+  def testRelativeChangeWithNegatives(self):
+    """Tests that relative change given is always positive."""
+    self.assertEqual(3.0, math_utils.RelativeChange(-1, 2))
+    self.assertEqual(3.0, math_utils.RelativeChange(1, -2))
+    self.assertEqual(1.0, math_utils.RelativeChange(-1, -2))
+
+
+if __name__ == '__main__':
+  unittest.main()