locustfile中的User类和HttpUser类

 

locustfile是什么?

locustfile是Locust性能测试工具的用户脚本,描述了单个用户的行为。

locustfile是个普通的Python模块,如果写作locustfile.py,那么路径切换到文件所在目录,直接执行命令就能运行:

$ locust

如果换个名字,那么只能通过-f参数指定文件名运行:

$ locust -f locust_files/my_locust_file.py

与一般Python模块不同的是:locustfile必须至少定义一个类,且继承自User类。

User类

User类表示性能测试的模拟用户,Locust会在运行时创建User类的实例

wait_time属性

设置等待时间,默认值不等待,立即执行。

Locust支持4种方式设置wait_time属性

  • constant函数,常量,任务执行完毕等待X秒开始下一任务。

    def constant(wait_time):
        """
        Returns a function that just returns the number specified by the wait_time argument
    
        Example::
    
            class MyUser(User):
                wait_time = constant(3)
        """
        return lambda instance: wait_time
    
  • between函数,区间随机值,任务执行完毕等待X-Y秒(中间随机取值)开始下一任务。

    def between(min_wait, max_wait):
        """
        Returns a function that will return a random number between min_wait and max_wait.
    
        Example::
    
            class MyUser(User):
                # wait between 3.0 and 10.5 seconds after each task
                wait_time = between(3.0, 10.5)
        """
        return lambda instance: min_wait + random.random() * (max_wait - min_wait)
    
  • constant_pacing函数,自适应,若任务耗时超过该时间,则任务结束后立即执行下一任务;若任务耗时不超过该时间,则等待达到该时间后执行下一任务。

    def constant_pacing(wait_time):
        """
        Returns a function that will track the run time of the tasks, and for each time it's
        called it will return a wait time that will try to make the total time between task
        execution equal to the time specified by the wait_time argument.
    
        In the following example the task will always be executed once every second, no matter
        the task execution time::
    
            class MyUser(User):
                wait_time = constant_pacing(1)
                @task
                def my_task(self):
                    time.sleep(random.random())
    
        If a task execution exceeds the specified wait_time, the wait will be 0 before starting
        the next task.
        """
    
        def wait_time_func(self):
            if not hasattr(self, "_cp_last_run"):
                self._cp_last_wait_time = wait_time
                self._cp_last_run = time()
                return wait_time
            else:
                run_time = time() - self._cp_last_run - self._cp_last_wait_time
                self._cp_last_wait_time = max(0, wait_time - run_time)
                self._cp_last_run = time()
                return self._cp_last_wait_time
    
        return wait_time_func
    
  • 自定义wait_time方法,比如每次等待时间1秒2秒3秒递增:

    class MyUser(User):
        last_wait_time = 0
    
        def wait_time(self):
            self.last_wait_time += 1
            return self.last_wait_time
    
        ...
    

weight属性

设置创建类实例的权重,默认每个类创建相同数量的实例。

locustfile中可以有多个继承了User类的类

通过weight属性可以让类更大概率创建实例,比如:

class WebUser(User):
    weight = 3
    ...

class MobileUser(User):
    weight = 1
    ...

WebUser类比MobileUser类多三倍概率创建实例。

host属性

设置URL前缀。

一般是在Locust的Web UI或者命令行,通过--host指定URL前缀。如果没有通过--host指定,并且类中设置了host属性,那么类的host属性才会生效。

environment属性

对用户运行环境的引用。

比如在task方法中通过environment属性终止运行:

self.environment.runner.quit()

on_start和on_stop方法

测试前初始化和测试后清理。

HttpUser类

开篇文章的示例脚本,没有继承User类,而是继承了它的子类HttpUser:

locustfile中的User类和HttpUser类-LMLPHP

它比User类更常用,因为它添加了一个client属性,用来发送HTTP请求

client属性/HttpSession

HttpUser类的client属性是HttpSession类的一个实例:

locustfile中的User类和HttpUser类-LMLPHP

HttpSession是requests.Session的子类,requests就是常用来做接口测试的那个requests库:

locustfile中的User类和HttpUser类-LMLPHP

HttpSession没有对requests.Session做什么改动,主要是传递请求结果给Locust,比如success/fail,response time,response length,name。

示例:

response = self.client.post("/login", {"username":"testuser", "password":"secret"})
print("Response status code:", response.status_code)
print("Response text:", response.text)
response = self.client.get("/my-profile")

由于requests.Session会暂存cookie,所以示例中登录/login请求后可以继续请求/my-profile

断言响应结果

可以使用with语句和catch_response参数对响应结果进行断言:

with self.client.get("/", catch_response=True) as response:
    if response.text == "Success":
        response.success()
    elif response.text != "Success":
        response.failure("Got wrong response")
    elif response.elapsed.total_seconds() > 0.5:
        response.failure("Request took too long")

或者直接抛出异常:

from locust.exception import RescheduleTask
...
with self.client.get("/does_not_exist/", catch_response=True) as response:
    if response.status_code == 404:
        raise RescheduleTask()

name参数

name参数用于把不同api按同一分组进行统计,比如:

for i in range(10):
    self.client.get("/blog?id=%i" % i, name="/blog?id=[id]")

会按/blog/?id=[id]统计1条数据,而不是分成10条数据。

HTTP代理

Locust默认设置了requests.Session的trust_env为False,不查找代理,以提高运行性能。如果需要可以设置locust_instance.client.trust_env为True。

示例代码

请求REST API并断言:

from json import JSONDecodeError
...
with self.client.post("/", json={"foo": 42, "bar": None}, catch_response=True) as response:
    try:
        if response.json()["greeting"] != "hello":
            response.failure("Did not get expected value in greeting")
    except JSONDecodeError:
        response.failure("Response could not be decoded as JSON")
    except KeyError:
        response.failure("Response did not contain expected key 'greeting'")

小结

locustfile是个普通Python模块,必须继承User类或其子类HttpUser等。本文对User类和HttpUser类的属性和方法进行了介绍,使用它们可以编写性能测试的用户脚本。locustfile还有另外一个重要组成元素,@task



 
06-07 20:38