Python unit-testing with nose: Making sequential tests

Question

I am just learning how to do unit-testing. I'm on Python / nose / Wing IDE.

(The project that I'm writing tests for is a simulations framework, and among other things it lets you run simulations both synchronously and asynchronously, and the results of the simulation should be the same in both.)

The thing is, I want some of my tests to use simulation results that were created in other tests. For example, synchronous_test calculates a certain simulation in synchronous mode, but then I want to calculate it in asynchronous mode, and check that the results came out the same.

How do I structure this? Do I put them all in one test function, or make a separate asynchronous_test? Do I pass these objects from one test function to another?

Also, keep in mind that all these tests will run through a test generator, so I can do the tests for each of the simulation packages included with my program.

Answer 1

In general, I'd recommend not making one test depend upon another. Do the synchronous_test, do the asynchronous_test, compare them each to the expected correct output, not to each other.

So something like:

class TestSimulate(TestCase):
    def setup(self):
        self.simpack = SimpackToTest()
        self.initial_state = pickle.load("initial.state")
        self.expected_state = pickle.load("known_good.state")

    def test_simulate(self):
        state = simulate(self.simpack, self.initial_state)
        # assert_equal will require State to implement __eq__ in a meaningful
        # way.  If it doesn't, you'll want to define your own comparison 
        # function.
        self.assert_equal(self.expected_state, state)

    def test_other_simulate(self):
        foo = OtherThing(self.simpack)
        blah = foo.simulate(self.initial_state)
        state = blah.state
        self.assert_equal(self.expected_state, state)

Answer 2

You can add tests that need to calculate once per class to the "setup" of that class. As an example:

from nose.tools import *
class Test_mysim():
    def setup(self):
        self.ans = calculate_it_once()

    def test_sync(self):
        ans=calculate_it_sync()
        assert_equal(ans,self.ans)

    def test_async(self):
        ans=calculate_it_async()
        assert_equal(ans,self.ans)