Friday, 24 September 2010

Autotest for IronPython

Continuing my explorations of IronPython, I decided I wanted a continuous test setup, which would automatically run my unit tests every time I saved a .py file, which was something I had seen on various “katacasts”. After a bit of investigation, I found the promising looking modipyd, which seemed to be Windows friendly. Unfortunately, github won’t let me download the files, so I set about creating my own basic continuous test tool for IronPython.

One advantage of using IronPython is that it immediately gives me access to the .NET framework’s FileSystemWatcher, which meant I didn’t have to worry about learning threading in Python. I did however have to work around one quirk which meant that the file changed event could get triggered multiple times, despite a single save command in my code editor.
Another challenge was working out how to load or reload a module given its name. This is done with the __import__ function, and using the sys.modules dictionary for the reload.

It took slightly longer than I hoped to get it fully working. Occasionally I get a spurious ValueError thrown when it attempts a reload. I’m not sure what that is all about. It should also be improved to rerun tests on all loaded modules not just the one that changed if you are not working entirely within a single file.
Again, any Python gurus feel free to suggest improvements.

import unittest
import clr
import sys
from System.IO import FileSystemWatcher
from System.IO import NotifyFilters
from System import DateTime

def changed(sender, args):
    global lastFileTimeWatcherEventRaised
    if DateTime.Now.Subtract(lastFileTimeWatcherEventRaised).TotalMilliseconds < 500:
    moduleName = args.Name[:-3]
    if reloadModule(moduleName):
    lastFileTimeWatcherEventRaised = DateTime.Now

def reloadModule(moduleName):
    loaded = False
            print 'Reloading ' + moduleName    
            print 'Importing ' + moduleName
        loaded = True
    except SyntaxError, s:
        print 'Syntax error loading ' + s.filename, 'line', s.lineno, 'offset', s.offset
        print s.text
        #sometimes get a ValueError here, not sure why
        error = sys.exc_info()[0]
        print error
    return loaded

def runTests(moduleName):
    loader = unittest.TestLoader()
    suite = loader.loadTestsFromModule(sys.modules[moduleName])
    if suite.countTestCases() > 0:
        runner = unittest.TextTestRunner()
        print 'No tests in module'

def watch(path):
    watcher = FileSystemWatcher()
    watcher.Filter = '*.py'
    watcher.Changed += changed
    watcher.Path = path
    watcher.NotifyFilter = NotifyFilters.LastWrite
    watcher.EnableRaisingEvents = 1
lastFileTimeWatcherEventRaised = DateTime.Now

if __name__ == '__main__':
    print 'Watching current folder for changes...'
    input('press Enter to exit')

If I get a chance I’ll record my own “katacast” showing the autotest python module in action.

Update: I've made the katacast. I've also made a slight improvement to the autotest code, moving the setting of lastFileTimeWatcherEventRaised further down to stop long-running tests thwarting the multiple-event filtering.

Post a Comment