Art of Unit Testing

Paul Moore gustav at morpheus.demon.co.uk
Sat Aug 18 14:19:04 CEST 2001


On Fri, 17 Aug 2001 11:32:49 -0700, Jeff Shannon <jeff at ccvcorp.com> wrote:

>Well, the alternative argument could be that, if you don't need to setup and
>teardown in between various tests, then they could be coded as subtests of a
>single, larger test...  OTOH, if you *do* have high setup/teardown overhead, which
>*does* require being redone for each test, then coding it each time would be a
>pain.  Lumping subtests together is easier than multiple copies of
>setup/teardown...

I'm not sure I agree. The long and short of it is that both cases can happen.
But look at my example "for real" (sort of)

class testSimpleQueries(unittest.TestCase):
    def setUp(self):
        # May take seconds to execute...
        self.connection = DB.Connect(connect_str)
    def tearDown(self):
        self.connection.Disconnect()
    def exec_query(self, q):
        "Trivial helper to run a query"
        return self.connection.Execute(q)
    def testQ1(self):
        "Simple query"
        q = "select 1 from dual"
        assertEqual(1, self.exec_query(q))
    def testQ2(self):
        "Exception when no rows returned"
        q = "select 1 from dual where 1=0"
        assertRaises(DB.Error, self.exec_query(q))
    # And 100 more trivial queries...

You get the idea. The setup costs a *lot* in relative terms of time (each test
query takes, say, 0.01 second). You really want to only do that once. But you
don't really want to code a single huge test - it destroys the reporting of the
individual test docstrings by unittest.main(). What do you do? I don't say it's
not possible to code this - just that the documentation doesn't make it clear
*how*.

Remember, I'm arguing that the common cases should be simple to code - not that
it's not possible to do these things. That makes people more likely to code unit
tests.

So really, I'm suggesting two things - (1) beef up the documentation of
unittest.main(), and give it a section to itself ("How to code a simple series
of unit tests"), and (2) if necessary, beef up unittest.main() to cater for such
common cases (I don't necessarily think this is required).

Paul.



More information about the Python-list mailing list