def METHOD_NAME(ls, v):
    """In this we test a *consequence* of the second invariant: When we insert
    a value into a list twice, the insertion point should be the same both
    times. This is because we know that v is > the previous element and == the
    next element.
    In theory if the former passes, this should always pass. In practice,
    failures are detected by this test with much higher probability because it
    deliberately puts the data into a shape that is likely to trigger a
    failure.
    This is an instance of a good general category of test: Testing how the
    function moves in responses to changes in the underlying data.
    """
    i = binary_search(ls, v)
    ls.insert(i, v)
    assert binary_search(ls, v) == i