I’ve been thinking about the issues involved with using IronPython in a product as a scripting language, internally we’ve already struggled at Syzmk with my love of refactoring breaking scripts in our deployed products left right and centre.
I think the problems I need to solve first are:
Regression tests for expected script usage is what it comes down… but if you sit down and start trying to write these tests in NUnit it all gets a bit unwieldy – there’s a lot of time wasted making sure your tabs are right, escaping characters correctly in strings, and running scripts, evaluating the results, and then asserting against them – it's frustrating, and fails to emulate the experience of your users who are writing scripts purely in Python.
So my next port of call was to try the unit testing support that comes with python (PyUnit) – it would definitely do the job – but then I need to do a couple of things… first I need to start bundling quite a few standard libraries with the scripting engine in our product, and then I have to write additional functionality to support capturing the results of running the PyUnit tests and presenting them to the automated build process… It's all sounding like a pain in the ass, and the automation build works nicely as it is, I’d rather not have to mess with it...
So I decided to do a little integration work, to see if I could run a test suite written in python as part of a C# assembly.
First off, my solutions user experience is ok – not perfect – but then I just wanted to make sure I could get it working, before I put any effort into cleaning it up, and not being an expert in extending NUnit, or coding python, it was probably doomed from the start to be a mediocre solution ;o)
The steps to get it working in a test assembly are:
First off, we write the fixture, the only requirements are:
Here’s an example fixture:
import System
from System import Console
class MyPythonFixture(NUnitFixture):
def testPass(self):
Console.WriteLine("--testPass--")
Assert.IsTrue(True)
def testFail(self):
Console.WriteLine("--testFail--")
Assert.IsTrue(False, "this will fail")
As you can see we are just using the existing NUnit Assert methods… There is one caveat to this that I will cover in another post (that of testing for expected exceptions).
Next we create a suite – which can wrap one or more python script files (included as assembly resources) – this is all we need to bridge the gap.
public class MyPythonSuite : AbstractPythonSuite
{
public MyPythonSuite()
: base("MyPythonFixture.py")
}
And last of all, we need to drop in a suite builder – in theory I should be able to include this in a support assembly – but it doesn’t seem to work, here’s the code:
[SuiteBuilder]
public class PythonSuiteExtensionBuilder : ISuiteBuilder
public TestSuite BuildFrom(Type type, int assemblyKey)
if (CanBuildFrom(type)) return new PythonSuiteExtension(type, assemblyKey);
return null;
public bool CanBuildFrom(Type type)
return (typeof(AbstractPythonSuite).IsAssignableFrom(type) && (type != typeof(AbstractPythonSuite)));
At this point when can test the assembly with NUnitGui, and see our python fixtures appear under the “MyPythonSuite”… pretty slick huh?
The big downsides of this approach are that you can’t run the tests individually using something like TestDriven.Net, and Resharper’s unit test window doesn’t pick them up… However NUnitGui and the corresponding NUnitConsole have no problems with them, and running all the tests in your assembly with TestDriven.Net does pick them up thankfully – so as long you don’t have many slow tests in your assembly it should still be tolerable (you can run them while still coding...).
And of course, they will be picked up in your automated builds – which is great news for me... I hate messing around with CruiseControl.Net's configuration.
I’ll tidy up the implementation a little and post the code soon.
