def testEmptyList(self): self.assertEqual([1, 2, 7], flatten([[1, 2], [], [7], []]))
def testSingleElement(self): self.assertEqual([1, 2, 2, 3, 7, 8, 7], flatten([[1, 2, 2, 3, 7, 8, 7]]))
def testFlatten(self): self.assertEqual([1, 2, 3, 7, 8], flatten([[1, 2], [3, 7], [8]]))
def testDuplicate(self): self.assertEqual([1, 2, 2, 3, 7, 8, 7], flatten([[1, 2], [2, 3], [7], [8, 7]]))