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有了 Jupyter、PyHamcrest，用一點測試的代碼把它們連在一起，你就可以教任何適用于單元測試的 Python 內(nèi)容。

關(guān)于 Ruby 社區(qū)的一些事情一直讓我印象深刻，其中兩個例子是對測試的承諾和對易于上手的強調(diào)。這兩方面最好的例子是 Ruby Koans，在這里你可以通過修復(fù)測試來學習 Ruby。

要是我們能把這些神奇的工具也用于 Python，我們應(yīng)該可以做得更好。是的，使用 Jupyter Notebook、PyHamcrest，再加上一點類似于膠帶的粘合代碼，我們可以做出一個包括教學、可工作的代碼和需要修復(fù)的代碼的教程。

首先，需要一些“膠布”。通常，你會使用一些漂亮的命令行測試器來做測試，比如 pytest 或 virtue。通常，你甚至不會直接運行它。你使用像 tox 或 nox 這樣的工具來運行它。然而，對于 Jupyter 來說，你需要寫一小段粘合代碼，可以直接在其中運行測試。

幸運的是，這個代碼又短又簡單：

import unittest
 
def run_test(klass):
    suite = unittest.TestLoader().loadTestsFromTestCase(klass)
    unittest.TextTestRunner(verbosity=2).run(suite)
    return klass

現(xiàn)在，裝備已經(jīng)就緒，可以進行第一次練習了。

在教學中，從一個簡單的練習開始，建立信心總是一個好主意。

那么，讓我們來修復(fù)一個非常簡單的測試：

@run_test
class TestNumbers(unittest.TestCase):
   
    def test_equality(self):
        expected_value = 3 # 只改這一行
        self.assertEqual(1+1, expected_value)

    test_equality (__main__.TestNumbers) ... FAIL
   
    ======================================================================
    FAIL: test_equality (__main__.TestNumbers)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-7-5ebe25bc00f3>", line 6, in test_equality
        self.assertEqual(1+1, expected_value)
    AssertionError: 2 != 3
   
    ----------------------------------------------------------------------
    Ran 1 test in 0.002s
   
    FAILED (failures=1)

“只改這一行” 對學生來說是一個有用的標記。它準確地表明了需要修改的內(nèi)容。否則，學生可以通過將第一行改為 return 來修復(fù)測試。

在這種情況下，修復(fù)很容易：

@run_test
class TestNumbers(unittest.TestCase):
   
    def test_equality(self):
        expected_value = 2 # 修復(fù)后的代碼行
        self.assertEqual(1+1, expected_value)

    test_equality (__main__.TestNumbers) ... ok
   
    ----------------------------------------------------------------------
    Ran 1 test in 0.002s
   
    OK

然而，很快，unittest 庫的原生斷言將被證明是不夠的。在 pytest 中，通過重寫 assert 中的字節(jié)碼來解決這個問題，使其具有神奇的屬性和各種啟發(fā)式方法。但這在 Jupyter notebook 中就不容易實現(xiàn)了。是時候挖出一個好的斷言庫了：PyHamcrest。

from hamcrest import *
@run_test
class TestList(unittest.TestCase):
   
    def test_equality(self):
        things = [1,
                  5, # 只改這一行
                  3]
        assert_that(things, has_items(1, 2, 3))

    test_equality (__main__.TestList) ... FAIL
   
    ======================================================================
    FAIL: test_equality (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-11-96c91225ee7d>", line 8, in test_equality
        assert_that(things, has_items(1, 2, 3))
    AssertionError:
    Expected: (a sequence containing <1> and a sequence containing <2> and a sequence containing <3>)
         but: a sequence containing <2> was <[1, 5, 3]>
   
   
    ----------------------------------------------------------------------
    Ran 1 test in 0.004s
   
    FAILED (failures=1)

PyHamcrest 不僅擅長靈活的斷言，它還擅長清晰的錯誤信息。正因為如此，問題就顯而易見了。[1, 5, 3] 不包含 2，而且看起來很丑：

@run_test
class TestList(unittest.TestCase):
   
    def test_equality(self):
        things = [1,
                  2, # 改完的行
                  3]
        assert_that(things, has_items(1, 2, 3))

    test_equality (__main__.TestList) ... ok
   
    ----------------------------------------------------------------------
    Ran 1 test in 0.001s
   
    OK

使用 Jupyter、PyHamcrest 和一點測試的粘合代碼，你可以教授任何適用于單元測試的 Python 主題。

例如，下面可以幫助展示 Python 從字符串中去掉空白的不同方法之間的差異。

source_string = "  hello world  "
 
@run_test
class TestList(unittest.TestCase):
   
    # 這是個贈品：它可以工作！
    def test_complete_strip(self):
        result = source_string.strip()
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world")))
 
    def test_start_strip(self):
        result = source_string # 只改這一行
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world  ")))
 
    def test_end_strip(self):
        result = source_string # 只改這一行
        assert_that(result,
                   all_of(starts_with("  hello"), ends_with("world")))

    test_complete_strip (__main__.TestList) ... ok
    test_end_strip (__main__.TestList) ... FAIL
    test_start_strip (__main__.TestList) ... FAIL
   
    ======================================================================
    FAIL: test_end_strip (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-16-3db7465bd5bf>", line 19, in test_end_strip
        assert_that(result,
    AssertionError:
    Expected: (a string starting with '  hello' and a string ending with 'world')
         but: a string ending with 'world' was '  hello world  '
   
   
    ======================================================================
    FAIL: test_start_strip (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-16-3db7465bd5bf>", line 14, in test_start_strip
        assert_that(result,
    AssertionError:
    Expected: (a string starting with 'hello' and a string ending with 'world  ')
         but: a string starting with 'hello' was '  hello world  '
   
   
    ----------------------------------------------------------------------
    Ran 3 tests in 0.006s
   
    FAILED (failures=2)

理想情況下，學生們會意識到 .lstrip() 和 .rstrip() 這兩個方法可以滿足他們的需要。但如果他們不這樣做，而是試圖到處使用 .strip() 的話：

source_string = "  hello world  "
 
@run_test
class TestList(unittest.TestCase):
   
    # 這是個贈品：它可以工作！
    def test_complete_strip(self):
        result = source_string.strip()
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world")))
 
    def test_start_strip(self):
        result = source_string.strip() # 改完的行
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world  ")))
 
    def test_end_strip(self):
        result = source_string.strip() # 改完的行
        assert_that(result,
                   all_of(starts_with("  hello"), ends_with("world")))

    test_complete_strip (__main__.TestList) ... ok
    test_end_strip (__main__.TestList) ... FAIL
    test_start_strip (__main__.TestList) ... FAIL
   
    ======================================================================
    FAIL: test_end_strip (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-17-6f9cfa1a997f>", line 19, in test_end_strip
        assert_that(result,
    AssertionError:
    Expected: (a string starting with '  hello' and a string ending with 'world')
         but: a string starting with '  hello' was 'hello world'
   
   
    ======================================================================
    FAIL: test_start_strip (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-17-6f9cfa1a997f>", line 14, in test_start_strip
        assert_that(result,
    AssertionError:
    Expected: (a string starting with 'hello' and a string ending with 'world  ')
         but: a string ending with 'world  ' was 'hello world'
   
   
    ----------------------------------------------------------------------
    Ran 3 tests in 0.007s
   
    FAILED (failures=2)

他們會得到一個不同的錯誤信息，顯示去除了過多的空白：

source_string = "  hello world  "
 
@run_test
class TestList(unittest.TestCase):
   
    # 這是個贈品：它可以工作！
    def test_complete_strip(self):
        result = source_string.strip()
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world")))
 
    def test_start_strip(self):
        result = source_string.lstrip() # Fixed this line
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world  ")))
 
    def test_end_strip(self):
        result = source_string.rstrip() # Fixed this line
        assert_that(result,
                   all_of(starts_with("  hello"), ends_with("world")))

    test_complete_strip (__main__.TestList) ... ok
    test_end_strip (__main__.TestList) ... ok
    test_start_strip (__main__.TestList) ... ok
   
    ----------------------------------------------------------------------
    Ran 3 tests in 0.005s
   
    OK