1. Kumar McMillan
  2. nose


nose /

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nose: a discovery-based unittest extension.

nose provides an alternate test discovery and running process for unittest, one that is intended to mimic the behavior of py.test as much as is reasonably possible without resorting to too much magic.

Basic usage

Use the nosetests script (after installation by setuptools):

nosetests [options] [(optional) test files or directories]

You may also use nose in a test script:

import nose

If you don't want the test script to exit with 0 on success and 1 on failure (like unittest.main), use nose.run() instead:

import nose
result = nose.run()

result will be true if the test run succeeded, or false if any test failed or raised an uncaught exception. Lastly, you can run nose.core directly, which will run nose.main():

python /path/to/nose/core.py

Please see the usage message for the nosetests script for information about how to control which tests nose runs, which plugins are loaded, and the test output.


Writing tests is easier

nose collects tests from unittest.TestCase subclasses, of course. But you can also write simple test functions, and test classes that are not subclasses of unittest.TestCase. nose also supplies a number of helpful functions for writing timed tests, testing for exceptions, and other common use cases. See Writing tests and Testing tools for more.

Running tests is easier

nose collects tests automatically, as long as you follow some simple guidelines for organizing your library and test code. There's no need to manually collect test cases into test suites. Running tests is also more responsive, since nose begins running tests as soon as the first test module is loaded. See Finding and running tests for more.

Setting up your test environment is easier

nose supports fixtures at the package, module, and test case level, so expensive initialization can be done as infrequently as possible. See Fixtures for more.

Doing what you want to do is easier

nose has plugin hooks for loading, running, watching and reporting on tests and test runs. If you don't like the default collection scheme, or it doesn't suit the layout of your project, or you need reports in a format different from the unittest standard, or you need to collect some additional information about tests (like code coverage or profiling data), you can write a plugin to do so. See Writing plugins for more.

Output capture

Unless called with the -s (--nocapture) switch, nose will capture stdout during each test run, and print the captured output only for tests that fail or have errors. The captured output is printed immediately following the error or failure output for the test. (Note that output in teardown methods is captured, but can't be output with failing tests, because teardown has not yet run at the time of the failure.)

Assert introspection

When run with the -d (--detailed-errors) switch, nose will try to output additional information about the assert expression that failed with each failing test. Currently, this means that names in the assert expression will be expanded into any values found for them in the locals or globals in the frame in which the expression executed.

In other words if you have a test like:

def test_integers():
    a = 2
    assert a == 4, "assert 2 is 4"

You will get output like:

File "/path/to/file.py", line XX, in test_integers:
      assert a == 4, "assert 2 is 4"
AssertionError: assert 2 is 4
  >>  assert 2 == 4, "assert 2 is 4"

Please note that dotted names are not expanded, and callables are not called in the expansion.

Setuptools integration

nose may be used with the setuptools test command. Simply specify nose.collector as the test suite in your setup file:

setup (
    # ...
    test_suite = 'nose.collector'

Then to find and run tests, you can run:

python setup.py test

When running under setuptools, you can configure nose settings via the environment variables detailed in the nosetests script usage message.

Please note that when run under the setuptools test command, some plugins will not be available, including the builtin coverage, profiler, and missed test plugins.

nose also includes its own setuptools command, nosetests, that provides support for all plugins and command line options, as well as configuration using the setup.cfg file. See nose.commands for more information about the nosetests command.

Writing tests

As with py.test, nose tests need not be subclasses of unittest.TestCase. Any function or class that matches the configured testMatch regular expression ((?:^|[b_.-])[Tt]est) by default) and lives in a module that also matches that expression will be run as a test. For the sake of compatibility with legacy unittest test cases, nose will also load tests from unittest.TestCase subclasses just like unittest does. Like py.test, functional tests will be run in the order in which they appear in the module file. TestCase derived tests and other test classes are run in alphabetical order.


nose supports fixtures (setup and teardown methods) at the package, module, and test level. As with py.test or unittest fixtures, setup always runs before any test (or collection of tests for test packages and modules); teardown runs if setup has completed successfully, whether or not the test or tests pass. For more detail on fixtures at each level, see below.

Test packages

nose allows tests to be grouped into test packages. This allows package-level setup; for instance, if you need to create a test database or other data fixture for your tests, you may create it in package setup and remove it in package teardown once per test run, rather than having to create and tear it down once per test module or test case.

To create package-level setup and teardown methods, define setup and/or teardown functions in the __init__.py of a test package. Setup methods may be named setup, setup_package, setUp, or setUpPackage; teardown may be named teardown, teardown_package, tearDown or tearDownPackage. Execution of tests in a test package begins as soon as the first test module is loaded from the test package.

Test modules

A test module is a python module that matches the testMatch regular expression. Test modules offer module-level setup and teardown; define the method setup, setup_module, setUp or setUpModule for setup, teardown, teardown_module, or tearDownModule for teardown. Execution of tests in a test module begins after all tests are collected.

Test classes

A test class is a class defined in a test module that is either a subclass of unittest.TestCase, or matches testMatch. Test classes that don't descend from unittest.TestCase are run in the same way as those that do: methods in the class that match testMatch are discovered, and a test case constructed to run each with a fresh instance of the test class. Like unittest.TestCase subclasses, other test classes may define setUp and tearDown methods that will be run before and after each test method.

Test functions

Any function in a test module that matches testMatch will be wrapped in a FunctionTestCase and run as a test. The simplest possible failing test is therefore:

def test():
    assert False

And the simplest passing test:

def test():

Test functions may define setup and/or teardown attributes, which will be run before and after the test function, respectively. A convenient way to do this, especially when several test functions in the same module need the same setup, is to use the provided with_setup decorator:

def setup_func():
    # ...

def teardown_func():
    # ...

@with_setup(setup_func, teardown_func)
def test():
    # ...

For python 2.3, add the attributes by calling the decorator function like so:

def test():
    # ...
test = with_setup(setup_func, teardown_func)(test)

or by direct assignment:

test.setup = setup_func
test.teardown = teardown_func

Test generators

nose supports test functions and methods that are generators. A simple example from nose's selftest suite is probably the best explanation:

def test_evens():
    for i in range(0, 5):
        yield check_even, i, i*3

def check_even(n, nn):
    assert n % 2 == 0 or nn % 2 == 0

This will result in 4 tests. nose will iterate the generator, creating a function test case wrapper for each tuple it yields. As in the example, test generators must yield tuples, the first element of which must be a callable and the remaining elements the arguments to be passed to the callable.

Setup and teardown functions may be used with test generators. The setup and teardown attributes must be attached to the generator function:

@with_setup(setup_func, teardown_func)
def test_generator():
    yield func, arg, arg ...

The setup and teardown functions will be executed for each test that the generator returns.

For generator methods, the setUp and tearDown methods of the class (if any) will be run before and after each generated test case.

Please note that method generators are not supported in unittest.TestCase subclasses.

Finding and running tests

nose, by default, follows a few simple rules for test discovery.

  • If it looks like a test, it's a test. Names of directories, modules, classes and functions are compared against the testMatch regular expression, and those that match are considered tests. Any class that is a unittest.TestCase subclass is also collected, so long as it is inside of a module that looks like a test.
  • Directories that don't look like tests and aren't packages are not inspected.
  • Packages are always inspected, but they are only collected if they look like tests. This means that you can include your tests inside of your packages (somepackage/tests) and nose will collect the tests without running package code inappropriately.
  • When a project appears to have library and test code organized into separate directories, library directories are examined first.
  • When nose imports a module, it adds that module's directory to sys.path; when the module is inside of a package, like package.module, it will be loaded as package.module and the directory of package will be added to sys.path.

Be aware that plugins and command line options can change any of those rules.

Testing tools

The nose.tools module provides a number of testing aids that you may find useful, including decorators for restricting test execution time and testing for exceptions, and all of the same assertX methods found in unittest.TestCase (only spelled in pep08 fashion, so assert_equal rather than assertEqual). See nose.tools for a complete list.

About the name

  • nose is the least silly short synonym for discover in the dictionary.com thesaurus that does not contain the word 'spy'.
  • Pythons have noses
  • The nose knows where to find your tests
  • Nose Obviates Suite Employment

Contact the author

You can email me at jpellerin+nose at gmail dot com.

To report bugs, ask questions, or request features, please use the issues tab at the Google code site: http://code.google.com/p/python-nose/issues/list. Patches are welcome!

Similar test runners

nose was inspired mainly by py.test, which is a great test runner, but formerly was not all that easy to install, and is not based on unittest.

Test suites written for use with nose should work equally well with py.test, and vice versa, except for the differences in output capture and command line arguments for the respective tools.