Add the best branching hill climbing algorithm.

BUG=None
TEST=unit testings for the pipeline stage, pipeline workers, generation,
steering, task, flag and hill climbing.

Change-Id: Ifd181f45c4b82f5fb77b0d4946757954aa806d33
Reviewed-on: https://gerrit-int.chromium.org/42284
Tested-by: Yuheng Long <yuhenglong@google.com>
Reviewed-by: Simon Que <sque@google.com>
Commit-Queue: Yuheng Long <yuhenglong@google.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/bestflags/generation.py b/bestflags/generation.py
index 7f0e94a1..0bc2f57c 100644
--- a/bestflags/generation.py
+++ b/bestflags/generation.py
@@ -107,19 +107,24 @@ class Generation(object):
     return True
 
   def Improve(self):
-    """True if this generation has improvement over its parent generation.
+    """True if this generation has improvement upon its parent generation.
 
     Raises:
       NoneOverridingError: The subclass should override this method.
     """
     raise NoneOverridingError('Must be implemented by child class')
 
-  def Next(self):
+  def Next(self, _):
     """Calculate the next generation.
 
     This is the core of the framework implementation. It must be overridden by
     the concrete subclass to implement algorithm specific generations.
 
+    Args:
+      _: A set of tasks that have been generated before. The overridden method
+        in the subclasses can use this so as not to generate task that has been
+        generated before.
+
     Returns:
       A set of new generations.