Brian uses the nose package for its testing framework. To check the code coverage of the test suite, we use coverage.py.

Running the test suite

The nosetests tool automatically finds tests in the code. When brian2 is in your Python path or when you are in the main brian2 directory, you can start the test suite with:

$ nosetests brian2 --with-doctest

This should show no errors or failures but possibly a number of skipped tests. The recommended way however is to import brian2 and call the test function, which gives you convenient control over which tests are run:

>>> import brian2
>>> brian2.test()

By default, this runs the test suite for all available (runtime) code generation targets. If you only want to test a specific target, provide it as an argument:

>>> brian2.test('numpy')

If you want to test several targets, use a list of targets:

>>> brian2.test(['weave', 'cython'])

In addition to the tests specific to a code generation target, the test suite will also run a set of independent tests (e.g. parsing of equations, unit system, utility functions, etc.). To exclude these tests, set the test_codegen_independent argument to False. Not all available tests are run by default, tests that take a long time are excluded. To include these, set long_tests to True.

To run the C++ standalone tests, you have to set the test_standalone argument to the name of a standalone device. If you provide an empty argument for the runtime code generation targets, you will only run the standalone tests:

>>> brian2.test([], test_standalone='cpp_standalone')

Checking the code coverage

To check the code coverage under Linux (with coverage and nosetests in your path) and generate a report, use the following commands (this assumes the source code of Brian with the file .coveragerc in the directory /path/to/brian):

$ coverage run --rcfile=/path/to/brian/.coveragerc $(which nosetests) --with-doctest brian2
$ coverage report

Using coverage html you can also generate a HTML report which will end up in the directory htmlcov.

Writing tests

Generally speaking, we aim for a 100% code coverage by the test suite. Less coverage means that some code paths are never executed so there’s no way of knowing whether a code change broke something in that path.

Unit tests

The most basic tests are unit tests, tests that test one kind of functionality or feature. To write a new unit test, add a function called test_... to one of the test_... files in the brian2.tests package. Test files should roughly correspond to packages, test functions should roughly correspond to tests for one function/method/feature. In the test functions, use assertions that will raise an AssertionError when they are violated, e.g.:

G = NeuronGroup(42, model='dv/dt = -v / (10*ms) : 1')
assert len(G) == 42

When comparing arrays, use the array_equal() function from numpy.testing.utils which takes care of comparing types, shapes and content and gives a nicer error message in case the assertion fails. Never make tests depend on external factors like random numbers – tests should always give the same result when run on the same codebase. You should not only test the expected outcome for the correct use of functions and classes but also that errors are raised when expected. For that you can use the assert_raises function (also in numpy.testing.utils) which takes an Exception type and a callable as arguments:

assert_raises(DimensionMismatchError, lambda: 3*volt + 5*second)

Note that you cannot simply write 3*volt + 5*second in the above example, this would raise an exception before calling assert_raises. Using a callable like the simple lambda expression above makes it possible for assert_raises to catch the error and compare it against the expected type. You can also check whether expected warnings are raised, see the documentation of the logging mechanism for details

For simple functions, doctests (see below) are a great alternative to writing classical unit tests.

By default, all tests are executed for all selected code generation targets (see Running the test suite above). This is not useful for all tests, some basic tests that for example test equation syntax or the use of physical units do not depend on code generation and need therefore not to be repeated. To execute such tests only once, they can be annotated with a codegen-independent attribute, using the attr decorator:

from nose.plugins.attrib import attr
from brian2 import NeuronGroup

def test_simple():
    # Test that the length of a NeuronGroup is correct
    group = NeuronGroup(5, '')
    assert len(group) == 5

Tests that are not “codegen-independent” are by default only executed for the runtimes device, i.e. not for the cpp_standalone device, for example. However, many of those tests follow a common pattern that is compatible with standalone devices as well: they set up a network, run it, and check the state of the network afterwards. Such tests can be marked as standalone-compatible, using the attr decorator in the same way as for codegen-independent tests. Since standalone devices usually have an internal state where they store information about arrays, array assignments, etc., they need to be reinitialized after such a test. For that use the with_setup decorator and provide the restore_device function as the teardown argument:

from nose import with_setup
from nose.plugins.attrib import attr
from numpy.testing.utils import assert_equal
from brian2 import *
from brian2.devices.device import restore_device

def test_simple_run():
    # Check that parameter values of a neuron don't change after a run
    group = NeuronGroup(5, 'v : volt')
    group.v = 'i*mV'
    assert_equal(group.v[:], np.arange(5)*mV)

As a rule of thumb:

  • If a test does not have a run call, mark it as codegen-independent
  • If a test has only a single run and only reads state variable values after the run, mark it as standalone-compatible and register the restore_device teardown function

Tests can also be written specifically for a standalone device (they then have to include the set_device and build calls explicitly). In this case tests have to be annotated with the name of the device (e.g. 'cpp_standalone') and with 'standalone-only' to exclude this test from the runtime tests. Also, the device should be restored in the end:

from nose import with_setup
from nose.plugins.attrib import attr
from brian2 import *
from brian2.devices.device import restore_device

@attr('cpp_standalone', 'standalone-only')
def test_cpp_standalone():
    # set up simulation
    # run simulation
    # check simulation results


Doctests are executable documentation. In the Examples block of a class or function documentation, simply write code copied from an interactive Python session (to do this from ipython, use %doctestmode), e.g.:

>>> expr = 'a*_b+c5+8+f(A)'
>>> print word_substitute(expr, {'a':'banana', 'f':'func'})

During testing, the actual output will be compared to the expected output and an error will be raised if they don’t match. Note that this comparison is strict, e.g. trailing whitespace is not ignored. There are various ways of working around some problems that arise because of this expected exactness (e.g. the stacktrace of a raised exception will never be identical because it contains file names), see the doctest documentation for details.

Doctests can (and should) not only be used in docstrings, but also in the hand-written documentation, making sure that the examples actually work. To turn a code example into a doc test, use the .. doctest:: directive, see Equations for examples written as doctests. For all doctests, everything that is available after from brian2 import * can be used directly. For everything else, add import statements to the doctest code or – if you do not want the import statements to appear in the document – add them in a .. testsetup:: block. See the documentation for Sphinx’s doctest extension for more details.

Doctests are a great way of testing things as they not only make sure that the code does what it is supposed to do but also that the documentation is up to date!

Test attributes

As explained above, the test suite can be run with different subsets of the available tests. For this, tests have to be annotated with the attr decorator available from nose.plugins.attrib. Currently, the following attributes are understood:

  • standalone: A C++ standalone test (not run by default when calling brian2.test())
  • codegen-independent: A test that does not use any code generation (run by default)
  • long: A test that takes a long time to run (not run by default)

Attributes can be simply given as a string argument to the attr decorator:

 from nose.plugins.attrib import attr

     pass  # ...

Correctness tests

[These do not exist yet for brian2]. Unit tests test a specific function or feature in isolation. In addition, we want to have tests where a complex piece of code (e.g. a complete simulation) is tested. Even if it is sometimes impossible to really check whether the result is correct (e.g. in the case of the spiking activity of a complex network), a useful check is also whether the result is consistent. For example, the spiking activity should be the same when using code generation for Python or C++. Or, a network could be pickled before running and then the result of the run could be compared to a second run that starts from the unpickled network.