三层各自的红绿

（每道题开头都有同一段：上面那套被测系统、unittest 和 mock，以及 eng_07 的静音 run(*cases)——交回「跑了几条/挂了几条/出错几条」。）

贯穿全条的被测系统（四段流水线）：

parse(line)            "苹果 3 2.5" → ("苹果", 3, 2.5)；不是三段就 raise ValueError
subtotal / discount    数量×单价；合计满 100 打九折
Store                  add(名, 数量, 单价)；total() = discount(各小计之和)
report(store, rate)    每样一行「名 数量 小计」，末行「合计 X 约 Y 外币」（Y = X / 汇率）
fetch_rate()           真的去连汇率服务——本地没网，一调就 ConnectionError
handle(lines, get_rate)  整条流水线：parse 每行 → Store → report(get_rate())

给三层各一条测试，跑在正确的 discount 和一个改坏的 discount（阈值写成 >100）上，看各层红绿：

import io, unittest
from unittest import mock

def parse(line):
    w = line.split()
    if len(w) != 3:
        raise ValueError("格式不对：" + line)
    return w[0], int(w[1]), float(w[2])


def subtotal(qty, price):
    return qty * price


def discount(amount):
    return amount * 0.9 if amount >= 100 else amount


class Store:
    def __init__(self):
        self.items = []

    def add(self, name, qty, price):
        self.items.append((name, qty, price))

    def total(self):
        return discount(sum(subtotal(q, p) for _, q, p in self.items))


def fmt(x):
    return ("%.2f" % x).rstrip("0").rstrip(".")


def report(store, rate):
    lines = [n + " " + str(q) + " " + fmt(subtotal(q, p)) for n, q, p in store.items]
    t = store.total()
    lines.append("合计 " + fmt(t) + " 约 " + fmt(t / rate) + " 外币")
    return "\n".join(lines)


def fetch_rate():
    raise ConnectionError("没有网络：汇率服务连不上")


def handle(lines, get_rate=fetch_rate):
    store = Store()
    for line in lines:
        n, q, p = parse(line)
        store.add(n, q, p)
    return report(store, get_rate())


def run(*cases):
    suite = unittest.TestSuite()
    for c in cases:
        suite.addTests(unittest.defaultTestLoader.loadTestsFromTestCase(c))
    r = unittest.TextTestRunner(stream=io.StringIO()).run(suite)
    return str(r.testsRun) + "/" + str(len(r.failures)) + "/" + str(len(r.errors))

SAMPLE = ["苹果 3 2.5", "西瓜 2 30", "米 10 4.2"]

def run_layers(disc):
    global discount
    old = discount
    discount = disc

    class U(unittest.TestCase):
        def test_parse(self):
            self.assertEqual(parse("苹果 3 2.5"), ("苹果", 3, 2.5))

    class I(unittest.TestCase):
        def test_total(self):
            s = Store()
            s.add("米", 10, 10)
            self.assertAlmostEqual(s.total(), 90)

    class E(unittest.TestCase):
        def test_full(self):
            self.assertTrue(handle(["米 10 10"], lambda: 1.0).endswith("合计 90 约 90 外币"))
    r = run(U) + "|" + run(I) + "|" + run(E)
    discount = old
    return r

print(run_layers(discount) + "//" + run_layers(lambda a: a * 0.9 if a > 100 else a))