'Tests that blank cards can be appended, and that future appends will
use blank cards when available (unless useblanks=False)'

def test_header_append_use_blanks(self):

    header = fits.Header([('A', 'B'), ('C', 'D')])
    header.append()
    header.append()
    assert (len(header) == 4)
    assert (header[(-1)] == '')
    assert (header[(-2)] == '')
    header.append(('E', 'F'))
    assert (len(header) == 4)
    assert (header[(-2)] == 'F')
    assert (header[(-1)] == '')
    header.append(('G', 'H'), useblanks=False)
    assert (len(header) == 5)
    assert (header[(-1)] == '')
    assert (header[(-2)] == 'H')
