【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

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。

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。



进行测试：

第1轮测试

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

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

运行测试并观察运行结果

lettuce

修改函数定义

def factorial(number):
return 1

再次运行测试并观察运行结果

lettuce

第2轮测试

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        

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。

运行测试并观察运行结果



修改函数定义

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

再次运行测试并观察运行结果



第3轮测试

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    

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。

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

修改函数定义



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 *

@step
def have_the_number(step, number):
'I have the number (\d+)'
world.number = int(number)

@step
def compute_its_factorial(step):
world.number = factorial(world.number)

@step
def 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 1
else:
return number*factorial(number-1)

用文档定义步骤

from lettuce import world, steps

@steps
class 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 = environs

def set_number(self, value):
self.environs.number = int(value)

def get_number(self):
return self.environs.number

def _assert_number_is(self, expected, msg="Got %d"):
number = self.get_number()
assert number == expected, msg % number

def 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。