def test_invalid():
w = NexusWriter()
with pytest.raises(ValueError):
w.write()
def test_write_with_no_data_but_trees():
nex = NexusWriter()
nex.trees.append('tree tree1 = (French,(English,Latin));')
content = nex.write()
assert re.search(r"BEGIN TREES", content)
assert re.search(r"tree tree1 = \(French,\(English,Latin\)\);", content)
