How to use the icecream.ic.prefix function in icecream

linePairs = []
    for line in lines:
        line = lineAfterContext(line, prefix)

        if not line:
            linePairs.append([])
            continue

        pairStrs = line.split(TEST_PAIR_DELIMITER)
        pairs = [tuple(s.split(':', 1)) for s in pairStrs]
        # Indented line of a multiline value.
        if len(pairs[0]) == 1 and line.startswith(' '):
            arg, value = linePairs[-1][-1]
            looksLikeAString = value[0] in ["'", '"']
            prefix = (arg + ': ') + (' ' if looksLikeAString else '')
            dedented = line[len(ic.prefix) + len(prefix):]
            linePairs[-1][-1] = (arg, value + '\n' + dedented)
        else:
            items = [
                (p[0].strip(), None) if len(p) == 1  # A value, like ic(3).
                else (p[0].strip(), p[1].strip())  # A variable, like ic(a).
                for p in pairs]
            linePairs.append(items)

    return linePairs

def stripPrefix(line):
    if line.startswith(ic.prefix):
        line = line.strip()[len(ic.prefix):]
    return line

def configureIcecreamOutput(prefix=None, outputFunction=None,
                            argToStringFunction=None, includeContext=None):
    oldPrefix = ic.prefix
    oldOutputFunction = ic.outputFunction
    oldArgToStringFunction = ic.argToStringFunction
    oldIncludeContext = ic.includeContext

    if prefix:
        ic.configureOutput(prefix=prefix)
    if outputFunction:
        ic.configureOutput(outputFunction=outputFunction)
    if argToStringFunction:
        ic.configureOutput(argToStringFunction=argToStringFunction)
    if includeContext:
        ic.configureOutput(includeContext=includeContext)

    yield

    ic.configureOutput(

def testOutputFunction(self):
        lst = []

        def appendTo(s):
            lst.append(s)

        with configureIcecreamOutput(ic.prefix, appendTo):
            with captureStandardStreams() as (out, err):
                ic(a)
        assert not out.getvalue() and not err.getvalue()

        with configureIcecreamOutput(outputFunction=appendTo):
            with captureStandardStreams() as (out, err):
                ic(b)
        assert not out.getvalue() and not err.getvalue()

        pairs = parseOutputIntoPairs(out, '\n'.join(lst), 2)
        assert pairs == [[('a', '1')], [('b', '2')]]

def testMultipleArgumentsLongLineWrapped(self):
        # A single long line with multiple variables is line wrapped.
        val = '*' * int(ic.lineWrapWidth / 4)
        valStr = ic.argToStringFunction(val)

        v1 = v2 = v3 = v4 = val
        with disableColoring(), captureStandardStreams() as (out, err):
            ic(v1, v2, v3, v4)

        pairs = parseOutputIntoPairs(out, err, 4)
        assert pairs == [[(k, valStr)] for k in ['v1', 'v2', 'v3', 'v4']]

        lines = err.getvalue().splitlines()
        assert (
            lines[0].startswith(ic.prefix) and
            lines[1].startswith(' ' * len(ic.prefix)) and
            lines[2].startswith(' ' * len(ic.prefix)) and
            lines[3].startswith(' ' * len(ic.prefix)))

def testMultipleArgumentsLongLineWrapped(self):
        # A single long line with multiple variables is line wrapped.
        val = '*' * int(ic.lineWrapWidth / 4)
        valStr = ic.argToStringFunction(val)

        v1 = v2 = v3 = v4 = val
        with disableColoring(), captureStandardStreams() as (out, err):
            ic(v1, v2, v3, v4)

        pairs = parseOutputIntoPairs(out, err, 4)
        assert pairs == [[(k, valStr)] for k in ['v1', 'v2', 'v3', 'v4']]

        lines = err.getvalue().splitlines()
        assert (
            lines[0].startswith(ic.prefix) and
            lines[1].startswith(' ' * len(ic.prefix)) and
            lines[2].startswith(' ' * len(ic.prefix)) and
            lines[3].startswith(' ' * len(ic.prefix)))