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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _count_relevant_tb_levels(tb):
 """Return the number of frames in ``tb`` before all that's left is unittest frames. Unlike its namesake in unittest, this doesn't bail out as soon as it hits a unittest frame, which means we don't bail out as soon as somebody uses the mock library, which defines ``__unittest``. """

    length = contiguous_unittest_frames = 0
    while tb:
        length += 1
        if _is_unittest_frame(tb):
            contiguous_unittest_frames += 1
        else:
            contiguous_unittest_frames = 0
        tb = tb.tb_next
    return length - contiguous_unittest_frames