Testing shell commands from Python

   如何測試shell命令?最近，我遇到了一些狀況，我想運行shell命令進行測試，Python稱爲萬能膠水語言,一些自動化測試均可以完成,目前手頭的工做都是用python完成的.可是沒法從Python中找到有關如何進行測試的教程。在google上搜索了好久以後，我找到了一個適合個人解決方案，也許它也適合你!

爲何使用Python進行測試?

您可使用專用工具來測試shell命令。爲何選擇Python而不是其餘語言或者工具?可是若是您常常使用Python，那麼使用Python是有意義的，由於Python已經包含了健壯的測試功能，這些功能很容易與其餘工具集成。經過測試Python中的shell命令，您能夠利用這些工具，並避免跟蹤不一樣地方的測試。另外，若是您已經熟悉用Python編寫測試，那麼爲shell命令編寫測試就變得垂手可得了。

Use cases

For the Netherlands eScience Center Python package template, I wanted tests to verify that the generated package can be installed, that the tests can be run, and that the documentation can be generated without errors. My Python text processing package nlppln contains CWL specifications of text mining tools, that can be validated by running them using a command line tool called cwltool. Another use case would be testing your package’s console scripts(although in this case it might be more convenient to use a package for creating command line interfaces that comes with built-in testing functionality, such as Click).

 

The sh package

You can run shell commands from Python using the subprocess module from the Python standard library. However, using this module is a hassle, because you have to do all the error handling yourself. Sh is a Python package that takes care of all that and allows you to run shell commands using a single line of code. If you want to run python setup.py install, all you have to do is:

import sh

sh.python(['setup.py', 'install'])

If you want to run foo and it is installed on your system, you can just do sh.foo().

Writing a test

So how can we use this for testing? Let’s look at an example. For the Python template, I want to test whether a project generated from the cookiecuttertemplate can be installed without errors. The goal of the template is to help users write high quality code with less effort, and having an installable empty project is a good first step. The code for the test that tests the installation is:

import pytest
import os
import sh

def test_install(cookies):
  # generate a temporary project using the cookiecutter
  # cookies fixture
  project = cookies.bake()                                                  

  # remember the directory where tests should be run from
  cwd = os.getcwd()
  # change directories to the generated project directory 
  # (the installation command must be run from here)
  os.chdir(str(project.project))

  try:
    # run the shell command
    sh.python(['setup.py', 'install'])
  except sh.ErrorReturnCode as e:
    # print the error, so we know what went wrong
    print(e)
    # make sure the test fails
    pytest.fail(e)
  finally:
    # always change directories to the test directory
    os.chdir(cwd)

That is all there is to it!

More examples

Of course there is a lot more you can do, e.g., checking whether files existafter running a shell command, or verifying the contents of generated files. What use cases can you come up with?

On Windows: use subprocess

Sh does not work on Windows. If you need to test shell commands on Windows, you are stuck with subprocess. Provenance tracking package recipycontains some nice examples of tests using subprocess that might help you on your way.

安裝sh

https://amoffat.github.io/sh/