Not understanding itertools.dropwhile()

[Jason Friedman]

<---- start code ---->

import itertools

data = """Line1
Line2

Line4
Line5"""

def test_to_start(s):
    return "2" in s

for line in itertools.dropwhile(test_to_start, data.splitlines()):
    print(line)

<---- end code ---->

I expect:

$ python3 dropwhile.py
Line2

Line4
Line5


I get:

$ python3 dropwhile.py
Line1
Line2

Line4
Line5


Please explain.
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