Add test for SelectDefaultBrowser and refactor implementation.

tools/telemetry/telemetry/core/backends/chrome/android_browser_finder_unittest.py

Index: tools/telemetry/telemetry/core/backends/chrome/android_browser_finder_unittest.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder_unittest.py b/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder_unittest.py
index 926ad1f5a6628f6135fd4253706e52af8d18939c..f180e3183d20d6b8e01221bd3776cfa882cc7cf5 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder_unittest.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder_unittest.py
@@ -87,3 +87,32 @@ class AndroidBrowserFinderTest(unittest.TestCase):
 
     browsers = android_browser_finder.FindAllAvailableBrowsers(finder_options)
     self.assertEquals(1, len(browsers))
+
+
+class FakePossibleBrowser(object):
+  def __init__(self, last_modification_time):
+    self._last_modification_time = last_modification_time
+
+  def last_modification_time(self):
+    return self._last_modification_time
+
+
+class SelectDefaultBrowserTest(unittest.TestCase):

[nednguyen, 2014/11/03 16:04:54]

+1 for test.

[slamm, 2014/11/03 16:25:55]

This worked nicely. I wrote the test and had it pass for the existing code.
Then, I refactored and made sure the test still worked.

+  def testEmptyListGivesNone(self):
+    self.assertIsNone(android_browser_finder.SelectDefaultBrowser([]))
+
+  def testSinglePossibleReturnsSame(self):
+    possible_browsers = [FakePossibleBrowser(last_modification_time=1)]
+    self.assertIs(
+      possible_browsers[0],
+      android_browser_finder.SelectDefaultBrowser(possible_browsers))
+
+  def testListGivesNewest(self):
+    possible_browsers = [
+        FakePossibleBrowser(last_modification_time=2),
+        FakePossibleBrowser(last_modification_time=3),  # newest
+        FakePossibleBrowser(last_modification_time=1),
+        ]
+    self.assertIs(
+      possible_browsers[1],
+      android_browser_finder.SelectDefaultBrowser(possible_browsers))