def is_cell_variable(trajectory, tests=1):
    """
    Simple test to check if cell changes.

    We compare the first frame to an integer number `tests` of other
    frames starting from the end of `trajectory`.
    """
    is_variable = False
    frames = len(trajectory)
    if tests > 0:
        skip = max(1, int(frames / float(tests)))
    else:
        skip = 1
    L0 = trajectory[0].cell.side
    for sample in range(frames - 1, 0, -skip):
        L1 = trajectory[sample].cell.side
        if L0[0] != L1[0] or L0[1] != L1[1] or L0[2] != L1[2]:
            is_variable = True
            break
    return is_variable
