【脚本语言系列】关于Python测试工具lettuce, 你需要知道的事

如何使用lettuce

• 安装lettuce(先安装Python2.7或者Python3.5、Python3.6)，即命令行输入以下命令：

pip install lettuce

1. 定义问题：给定一个数，如何计算它的阶乘？
   注意：只有非负整数才有阶乘，0的阶乘为1。
2. 项目结构：新建文件夹feautures，其内新建空文件steps.py以及空文件zero.feature。
   注意：文件名可以改变，feautures文件夹名以及其内文件的后缀名不能改变。lettuce将会在features文件夹中递归查找.py以及.feature。
   

3. 进行测试：

   • 第1轮测试

     1. 描述行为，即用英文在zero.feature文件中描述预期行为
        

         Feature: Compute factorial  In order to play with Lettuce  As beginners  We'll implement factorial  Scenario: Factorial of 0    Given I have the number 0    When I compute its factorial    Then I see the number 1

     2. 用python定义步骤，即创建包含有描述步骤的python代码的steps.py文件
        现在有了测试方案的各步骤定义，因而Lettuce能够理解行为描述。
        

        from lettuce import *@step('I have the number (\d+)')def have_the_number(step, number):    world.number = int(number)@step('I compute its factorial')def compute_its_factorial(step):    world.number = factorial(world.number)@step('I see the number (\d+)')def check_number(step, expected):    expected = int(expected)    assert world.number == expected, \        "Got %d" % world.number

        定义被测函数，即在其他位置（非steps.py）中定义被测函数
        

            def factorial(number):        return -1

     3. 运行测试并观察运行结果
        

        lettuce

     4. 修改函数定义
        

        def factorial(number):    return 1

     5. 再次运行测试并观察运行结果
        

        lettuce

   • 第2轮测试

     1. 描述行为
        

         Feature: Compute factorial  In order to play with Lettuce  As beginners  We'll implement factorial  Scenario: Factorial of 0    Given I have the number 0    When I compute its factorial    Then I see the number 1  Scenario: Factorial of 1    Given I have the number 1    When I compute its factorial    Then I see the number 1  Scenario: Factorial of 2    Given I have the number 2    When I compute its factorial    Then I see the number 2        

     2. 用python定义步骤
        在第1次测试基础上不需要进行修改。
        定义被测函数
        在第1次测试基础上不需要进行修改。

     3. 运行测试并观察运行结果
        

     4. 修改函数定义
        

        def factorial(number):   number = int(number)   if (number == 0) or (number == 1):       return 1   else:       return number

     5. 再次运行测试并观察运行结果
        

   • 第3轮测试

     1. 描述行为
        

         Feature: Compute factorial  In order to play with Lettuce  As beginners  We'll implement factorial  Scenario: Factorial of 0    Given I have the number 0    When I compute its factorial    Then I see the number 1  Scenario: Factorial of 1    Given I have the number 1    When I compute its factorial    Then I see the number 1  Scenario: Factorial of 2    Given I have the number 2    When I compute its factorial    Then I see the number 2   Scenario: Factorial of 3    Given I have the number 3    When I compute its factorial    Then I see the number 6     Scenario: Factorial of 4    Given I have the number 4    When I compute its factorial    Then I see the number 24    

     2. 用python定义步骤
        在第1次测试基础上不需要进行修改。
        定义被测函数
        在第1次测试基础上不需要进行修改。

     3. 运行测试并观察运行结果
        

        def factorial(number):   number = int(number)   if (number == 0) or (number == 1):       return 1   else:       return number

     4. 修改函数定义
        

     5. 再次运行测试并观察运行结果
        

   • 第4轮测试
     语法糖：函数名以及文档现在能够描述步骤语句；0.2.19版本以上支持。由函数名和函数文档来构造步骤语句，只需用不含有参数的”@step”标识符对函数进行装饰。以下的两个例子，分别以函数名以及文档进行描述，其本质与以上的例子相同。

     • 用函数名定义步骤
       

       from lettuce import *@stepdef have_the_number(step, number):'I have the number (\d+)'world.number = int(number)@stepdef compute_its_factorial(step):world.number = factorial(world.number)@stepdef check_number(step, expected):'I see the number (\d+)'expected = int(expected)assert world.number == expected, \    "Got %d" % world.number  def factorial(number):number = int(number)if (number == 0) or (number == 1):    return 1else:    return number*factorial(number-1)

     • 用文档定义步骤
       

       from lettuce import world, steps@stepsclass FactorialSteps(object):    """Methods in exclude or starting with _ will not be considered as step"""exclude = ['set_number', 'get_number']def __init__(self, environs):    self.environs = environsdef set_number(self, value):    self.environs.number = int(value)def get_number(self):    return self.environs.numberdef _assert_number_is(self, expected, msg="Got %d"):    number = self.get_number()    assert number == expected, msg % numberdef have_the_number(self, step, number):    '''I have the number (\d+)'''    self.set_number(number)def i_compute_its_factorial(self, step):    number = self.get_number()    self.set_number(factorial(number))def check_number(self, step, expected):    '''I see the number (\d+)'''    self._assert_number_is(int(expected))# Important!# Steps are added only when you instanciate the "@steps" decorated class# Internally decorator "@steps" build a closure with __init__FactorialSteps(world)def factorial(number):    number = int(number)    if (number == 0) or (number == 1):        return 1    else:        return number*factorial(number-1)                

什么是lettuce

lettuce是基于BDD（行为驱动开发）理念下非常有用和迷人的工具。
它可以执行纯文本功能描述用作Python项目的自动化测试，就像Cucumber对 Ruby一样。
lettuce使得开发和测试过程非常简单，可扩展，易读，而且最好的是，它允许不编程的人描述某个系统的行为，不需要想像这些描述会在开发过程中自动测试系统。