def f():
base = TWriter()
filter = streamio.TextOutputFilter(base, linesep="\n")
filter.write("x" * 100)
filter.seek(50, 0)
filter.write("y" * 10)
assert base.buf == "x" * 50 + "y" * 10 + "x" * 40
def f():
base = TWriter()
filter = streamio.TextOutputFilter(base, linesep="\n")
filter.write("abc")
filter.write("def\npqr\nuvw")
filter.write("\n123\n")
assert base.buf == "abcdef\npqr\nuvw\n123\n"
def f():
base = TWriter()
filter = streamio.TextOutputFilter(base, linesep="\r\n")
filter.write("xxx")
assert filter.tell() == 3
filter.write("\nabc\n")
assert filter.tell() == 10