复现 bug 的测试红了

length 里 cm 的系数被写成了 0.1。写一条按用户报告复现的测试，运行程序：

import io, unittest

LEN = {"m": 1.0, "km": 1000.0, "cm": 0.1}

def length(v, src, to):
    return v * LEN[src] / LEN[to]

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))

class TestBug(unittest.TestCase):
    def test_cm_to_m(self):
        self.assertAlmostEqual(length(42, "cm", "m"), 0.42)

print(run(TestBug) + "/" + str(length(42, "cm", "m")))