单元测试框架处理多组数据的另一种写法：基于构造函数和超继承

众所周知，在单元测试框架中引入ddt，可以将一组数据分解为多组数据，从而实现一条数据对应一个测试用例。但是除此之外，有没有别的办法来实现这个目的呢？

一. 代码部分

1. 创建一个被测函数math_method.py

class MethMethod():
    def add_test(self,a,b):
        return (a+b)

2. 创建测试用例test_math_method.py

import unittest
from homework.math_method import MethMethod


#测试类

class TestMathMethod(unittest.TestCase):

    def __init__(self, methodName, a, b, expected):
        super(TestMethMethod, self).__init__(methodName)
        self.a = a
        self.b = b
        self.expected = expected

    #测试用例

    def test_add(self):
        try:

            self.assertEqual(result, self.expected)
        except Exception:
            print("出错了")
        else:
            print("计算结果是:{}".format(result))

3. 创建测试数据test_data.txt

[{"a":2,"b":3,"expected":5},{"a":-1,"b":-2,"expected":-3},{"a":3,"b":-1,"expected":-2},{"a":-3,"b":-1,"expected":-4}]

4. 创建测试集test_suite.py

import unittest
from homework.test_math_method import TestMathMethod
import HTMLTestRunnerNew

fs= open("test_data.txt")
datas = fs.read()
datas = eval(datas)
print(type(datas))


if __name__ == '__main__':

    suite=unittest.TestSuite()
    for item in datas:
        suite.addTest(TestMathMethod("test_add", item['a'], item['b'], item['expected']))
    file=open("test_report.html","wb+")
    runner=HTMLTestRunnerNew.HTMLTestRunner(file,title="加法单元测试报告",tester="july")
    runner.run(suite)

二. 代码分析

1. 测试用例类中需要定义一个构造函数，这个构造函数继承了父类的属性，也就是unittest.TestCase的methodName参数

同时，在子类中也重写了构造函数，添加了参数a, b, expected，而这三个则是测试用例函数test_add需要用到的

class TestMethMethod(unittest.TestCase):

    def __init__(self, methodName, a, b, expected):
        super(TestMethMethod, self).__init__(methodName)
        self.a = a
        self.b = b
        self.expected = expected

请看TestCase的源码

class TestCase(object):


    failureException = AssertionError

    longMessage = True

    maxDiff = 80*8

    # If a string is longer than _diffThreshold, use normal comparison instead
    # of difflib.  See #11763.
    _diffThreshold = 2**16

    # Attribute used by TestSuite for classSetUp

    _classSetupFailed = False

    def __init__(self, methodName='runTest'):
        """Create an instance of the class that will use the named test
           method when executed. Raises a ValueError if the instance does
           not have a method with the specified name.
        """
        self._testMethodName = methodName
        self._outcome = None
        self._testMethodDoc = 'No test'
        try:
            testMethod = getattr(self, methodName)
        except AttributeError:
            if methodName != 'runTest':
                # we allow instantiation with no explicit method name
                # but not an *incorrect* or missing method name
                raise ValueError("no such test method in %s: %s" %
                      (self.__class__, methodName))
        else:
            self._testMethodDoc = testMethod.__doc__
        self._cleanups = []
        self._subtest = None

2. 此时回到测试集中，看下面一段，TestMathMethod类中本来只有一个参数，methodName，也就是测试用例名，但此时的TestMathMethod已经被我们改写了：不仅继承了父类的methodName方法，而且构造函数中新增了三个参数a, b, expected，这样我们在收集测试用例时，可以为TestMathMethod类添加四个参数：methodName, a, b, expected。通过for循环遍历一组数据，这样可以将多组数据作为多个测试用例添加到测试集中

for item in datas:
        suite.addTest(TestMathMethod("test_add", item['a'], item['b'], item['expected']))

三. 比较

ddt的方法：简单，因为涉及到装饰器，不易理解

构造函数：略显繁琐，但容易理解