input: Write a function to generate a 5x5 matrix filled with zeros.
  assert generate_matrix() == [[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
  assert isinstance(generate_matrix(), list)
  assert all(isinstance(row, list) and len(row) == 5 for row in generate_matrix())
output: def generate_matrix():
      return [[0, 0, 0, 0, 0] for _ in range(5)]