import unittest


def build_suite(classes):
  """Creates a TestSuite for all unit test classes in the list.
  
  Assumes that each of the classes in the list has unit test methods which
  begin with 'test'. Calls unittest.makeSuite.

  Returns: 
    A new unittest.TestSuite containing a test suite for all classes.   
  """
  suites = [unittest.makeSuite(a_class, 'test') for a_class in classes]
  return unittest.TestSuite(suites)