text: import unittest
  from exercises import n_queens
  
  
  class TestNQueens(unittest.TestCase):
      def test_no_solution(self):
          self.assertFalse(n_queens(2))
          self.assertFalse(n_queens(3))
  
      def test_valid_solution(self):
          self.assertTrue(n_queens(1))  # e.g. [(0, 0)]
          self.assertTrue(n_queens(4))  # e.g. [(0, 1), (1, 3), (2, 0), (3, 2)]
  
          # This might take a while (at most n^3 possible solutions)
          # e.g. [(0, 0), (1, 4), (2, 7), (3, 5), (4, 2), (5, 6), (6, 1), (7, 3)]
          # self.assertTrue(n_queens(8))
  
  
  if __name__ == '__main__':
      unittest.main()
  