Temporary directories and files

The ‘tmpdir’ test function argument

You can use the tmpdir function argument which will provide a temporary directory unique to the test invocation, created in the base temporary directory.

tmpdir is a py.path.local object which offers os.path methods and more. Here is an example test usage:

# content of test_tmpdir.py
import os
def test_create_file(tmpdir):
    p = tmpdir.mkdir("sub").join("hello.txt")
    p.write("content")
    assert p.read() == "content"
    assert len(tmpdir.listdir()) == 1
    assert 0

Running this would result in a passed test except for the last assert 0 line which we use to look at values:

$ py.test test_tmpdir.py
=========================== test session starts ============================
platform linux -- Python 3.4.1 -- py-1.4.27 -- pytest-2.7.1
rootdir: /tmp/doc-exec-118, inifile:
collected 1 items

test_tmpdir.py F

================================= FAILURES =================================
_____________________________ test_create_file _____________________________

tmpdir = local('/tmp/pytest-19/test_create_file0')

    def test_create_file(tmpdir):
        p = tmpdir.mkdir("sub").join("hello.txt")
        p.write("content")
        assert p.read() == "content"
        assert len(tmpdir.listdir()) == 1
>       assert 0
E       assert 0

test_tmpdir.py:7: AssertionError
========================= 1 failed in 0.04 seconds =========================

The default base temporary directory

Temporary directories are by default created as sub-directories of the system temporary directory. The base name will be pytest-NUM where NUM will be incremented with each test run. Moreover, entries older than 3 temporary directories will be removed.

You can override the default temporary directory setting like this:

py.test --basetemp=mydir

When distributing tests on the local machine, pytest takes care to configure a basetemp directory for the sub processes such that all temporary data lands below a single per-test run basetemp directory.