[Telemetry] Fix @Cache to maintain cache for life of instance for bound methods

tools/telemetry/telemetry/unittest/decorators_unittest.py

Index: tools/telemetry/telemetry/unittest/decorators_unittest.py
diff --git a/tools/telemetry/telemetry/unittest/decorators_unittest.py b/tools/telemetry/telemetry/unittest/decorators_unittest.py
index 0487f3475aad2c6585adcd4ba1317ffb0e23ff28..45c56af1380f2826a23561aede982d38f7f7331a 100644
--- a/tools/telemetry/telemetry/unittest/decorators_unittest.py
+++ b/tools/telemetry/telemetry/unittest/decorators_unittest.py
@@ -7,8 +7,15 @@ import unittest
 from telemetry import decorators
 
 
+_counter = 0
+
+
 class Foo(object):
-  pass
+  @decorators.Cache
+  def GetCountCached(self, _):
+    global _counter
+    _counter = _counter + 1
+    return _counter
 
 
 def CreateFooUncached(_):
@@ -21,6 +28,7 @@ def CreateFooCached(_):
 
 
 class DecoratorsUnitTest(unittest.TestCase):
+  # pylint: disable=C0102
 
   def testCacheDecorator(self):
     self.assertNotEquals(CreateFooUncached(1), CreateFooUncached(2))
@@ -28,3 +36,24 @@ class DecoratorsUnitTest(unittest.TestCase):
 
     self.assertNotEquals(CreateFooUncached(1), CreateFooUncached(1))
     self.assertEquals(CreateFooCached(1), CreateFooCached(1))
+
+  def testCacheableMemberCachesOnlyForSameArgs(self):
+    foo = Foo()
+    value_of_one = foo.GetCountCached(1)
+
+    self.assertEquals(value_of_one, foo.GetCountCached(1))
+    self.assertNotEquals(value_of_one, foo.GetCountCached(2))
+
+  def testCacheableMemberHasSeparateCachesForSiblingInstances(self):
+    foo = Foo()
+    sibling_foo = Foo()
+
+    self.assertNotEquals(foo.GetCountCached(1), sibling_foo.GetCountCached(1))
+
+  def testCacheableMemberHasSeparateCachesForNextGenerationInstances(self):
+    foo = Foo()
+    last_generation_count = foo.GetCountCached(1)
+    foo = None
+    foo = Foo()
+
+    self.assertNotEquals(last_generation_count, foo.GetCountCached(1))