import unittest
from simple_calculator import SimpleCalculator

class AdditionTestSuite(unittest.TestCase):
    def setUp(self):
        """ Executed before every test case """
        self.calculator = SimpleCalculator()

    def tearDown(self):
        """ Executed after every test case """
        print("\ntearDown executing after the test case. Result:")

    def test_addition_two_integers(self):
        result = self.calculator.sum(5, 6)
        self.assertEqual(result, 11)

    def test_addition_integer_string(self):
        result = self.calculator.sum(5, "6")
        self.assertEqual(result, "ERROR")

    def test_addition_negative_integers(self):
        result = self.calculator.sum(-5, -6)
        self.assertEqual(result, -11)
        self.assertNotEqual(result, 11)

# Execute all the tests when the file is executed
if __name__ == "__main__":
    unittest.main()

$ python3 test_simple_calulator.py

tearDown executing after the test case. Result:
E
tearDown executing after the test case. Result:
E
tearDown executing after the test case. Result:
E
======================================================================
ERROR: test_addition_integer_string (__main__.AdditionTestSuite)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_simple_calulator.py", line 22, in test_addition_integer_string
    result = self.calculator.sum(5, "6")
AttributeError: 'SimpleCalculator' object has no attribute 'sum'

======================================================================
ERROR: test_addition_negative_integers (__main__.AdditionTestSuite)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_simple_calulator.py", line 26, in test_addition_negative_integers
    result = self.calculator.sum(-5, -6)
AttributeError: 'SimpleCalculator' object has no attribute 'sum'

======================================================================
ERROR: test_addition_two_integers (__main__.AdditionTestSuite)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_simple_calulator.py", line 18, in test_addition_two_integers
    result = self.calculator.sum(5, 6)
AttributeError: 'SimpleCalculator' object has no attribute 'sum'

----------------------------------------------------------------------
Ran 3 tests in 0.001s

FAILED (errors=3)

class SimpleCalculator:
    def sum(self, a, b):
        """ Function to add two integers """
        return a + b

现在，我们的计算器已准备好将两个数字相加，但是要确保它能按预期运行，请让我们tearDown()从测试中删除该函数，然后再次运行测试：

$ python3 test_simple_calulator.py
E..
======================================================================
ERROR: test_addition_integer_string (__main__.AdditionTestSuite)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_simple_calulator.py", line 22, in test_addition_integer_string
    result = self.calculator.sum(5, "6")
  File "/Users/robley/Desktop/code/python/unittest_demo/src/simple_calculator.py", line 7, in sum
    return a + b
TypeError: unsupported operand type(s) for +: 'int' and 'str'

----------------------------------------------------------------------
Ran 3 tests in 0.002s

FAILED (errors=1)

我们的错误已从3个减少到只有1个。第一行的报告摘要E..指示一个测试导致错误并且无法完成执行，其余两项通过。为了进行第一次测试，我们必须重构求和函数，如下所示：

    def sum(self, a, b):
        if isinstance(a, int) and isinstance(b, int):
            return a + b

当我们再运行一​​次测试时：

$ python3 test_simple_calulator.py
F..
======================================================================
FAIL: test_addition_integer_string (__main__.AdditionTestSuite)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_simple_calulator.py", line 23, in test_addition_integer_string
    self.assertEqual(result, "ERROR")
AssertionError: None != 'ERROR'

----------------------------------------------------------------------
Ran 3 tests in 0.001s

FAILED (failures=1)

这次，我们的sum函数执行完成，但是测试失败。这是因为当输入之一不是整数时，我们没有返回任何值。我们的断言与之比较None，ERROR并且由于它们不相等，因此测试失败。为了使测试通过，我们必须在sum()函数中返回错误：

def sum(self, a, b):
    if isinstance(a, int) and isinstance(b, int):
        return a + b
    else:
        return "ERROR"

当我们运行测试时：

$ python3 test_simple_calulator.py
...
----------------------------------------------------------------------
Ran 3 tests in 0.000s

OK

现在，我们所有的测试都通过了，我们获得了3个完全停止信号，以表明我们所有3个关于附加功能的测试都通过了。减法，乘法和除法测试套件也以类似的方式实现。

我们还可以测试是否引发异常。例如，当数字除以零时，ZeroDivisionError会引发异常。在我们的中DivisionTestSuite，我们可以确认是否引发了异常：

class DivisionTestSuite(unittest.TestCase):
    def setUp(self):
        """ Executed before every test case """
        self.calculator = SimpleCalculator()

    def test_divide_by_zero_exception(self):
        with self.assertRaises(ZeroDivisionError):
            self.calculator.divide(10, 0)

该test_divide_by_zero_exception()会执行divide(10, 0)该异常确实提高了我们的计算器和确认的功能。我们可以DivisionTestSuite隔离执行，如下所示：

$ python3 -m unittest test_simple_calulator.DivisionTestSuite.test_divide_by_zero_exception
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

完整的除法功能测试套件可在下面的要点中找到，用于乘法和减法功能的测试套件。

结论

在本文中，我们探索了该unittest框架并确定了在开发Python程序时使用该框架的情况。与其他测试框架相反，该unittest框架(也称为PyUnit)在默认情况下随附Python发行版。在TDD方式中，我们为一个简单的计算器编写了测试，执行了测试，然后实现了使测试通过的功能。

该unittest框架提供了创建和组合测试用例的功能，并根据预期输出检查计算器的输出以验证其是否按预期工作。