前言
写完一个项目的自动化用例之后，发现有些用例运行较慢，影响整体的用例运行速度，于是领导说找出运行慢的那几个用例优化下。 –durations 参数可以统计出每个用例运行的时间，对用例的时间做个排序。
–durations=N pytest -h 查看命令行参数，关于 --durations=N 参数的使用方式
>pytest -h
reporting:
--durations=N show N slowest setup/test durations (N=0 for all).
当 N=0 的时候显示全部用例的运行时间
–durations=0
先写几个pytest的用例，在用例里面加sleep时间，这样方便看到每个用例运行的持续时间
import pytest
import time
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# blog地址 https://www.cnblogs.com/yoyoketang/
@pytest.fixture()
def set_up_fixture():
time.sleep(0.1)
yield
time.sleep(0.2)
def test_01(set_up_fixture):
print("用例1")
time.sleep(1.0)
def test_02(set_up_fixture):
print("用例2")
time.sleep(0.6)
def test_03(set_up_fixture):
print("用例3")
time.sleep(1.2)
def test_04(set_up_fixture):
print("用例4")
time.sleep(0.3)
def test_05(set_up_fixture):
print("用例5")
time.sleep(2.3)
当 N=0 的时候显示全部用例的运行时间
>pytest test_dur.py --durations=0 -v
============================= test session starts =============================
collected 5 items
test_dur.py::test_01 PASSED [ 20%]
test_dur.py::test_02 PASSED [ 40%]
test_dur.py::test_03 PASSED [ 60%]
test_dur.py::test_04 PASSED [ 80%]
test_dur.py::test_05 PASSED [100%]
=========================== slowest test durations ============================
2.30s call test_dur.py::test_05
1.20s call test_dur.py::test_03
1.00s call test_dur.py::test_01
0.60s call test_dur.py::test_02
0.30s call test_dur.py::test_04
0.20s teardown test_dur.py::test_05
0.20s teardown test_dur.py::test_01
0.20s teardown test_dur.py::test_02
0.20s teardown test_dur.py::test_03
0.20s teardown test_dur.py::test_04
0.10s setup test_dur.py::test_03
0.10s setup test_dur.py::test_01
0.10s setup test_dur.py::test_02
0.10s setup test_dur.py::test_05
0.10s setup test_dur.py::test_04
========================== 5 passed in 7.05 seconds ===========================
用例运行的时候会经历3个阶段：setup,call,teardown。call就是测试用例，setup和teardown就是用例的fixture部分。
–durations=3如果我们只需要筛选出运行时间最慢的3条用例，可以设置–durations=3
>pytest test_dur.py --durations=3 -v
============================= test session starts =============================
collected 5 items
test_dur.py::test_01 PASSED [ 20%]
test_dur.py::test_02 PASSED [ 40%]
test_dur.py::test_03 PASSED [ 60%]
test_dur.py::test_04 PASSED [ 80%]
test_dur.py::test_05 PASSED [100%]
========================== slowest 3 test durations ===========================
2.30s call test_dur.py::test_05
1.20s call test_dur.py::test_03
1.00s call test_dur.py::test_01
========================== 5 passed in 7.00 seconds ===========================
这样就可以对运行慢的用例针对性优化。 
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