PyModel is an open-source model-based testing framework in Python. Code, documents, and downloads are available: http://staff.washington.edu/jon/pymodel/www/ In unit testing, the programmer codes the test cases, and also codes assertions that check whether each test case passed. In model-based testing, the programmer codes a "model" that generates as many test cases as desired and also acts as the oracle that checks the cases. PyModel supports on-the-fly testing, which can generate indefinitely long nonrepeating tests as the test run executes. PyModel can focus test cases on scenarios of interest by composition, a versatile technique that combines models by synchronizing shared actions and interleaving unshared actions. PyModel can guide test coverage according to programmable strategies coded by the programmer. PyModel provides three programs: - pma, pymodel analyzer: generates a finite state machine (FSM) and computes properties by exploring a model program, FSM, test suite, or a product of these. - pmg, pymodel graphics: generates a file of graphic commands from an FSM. - pmt, pymodel tester: displays traces, generates tests offline, executes offline tests, or generates and executes tests on-the-fly. Use pma and pmg to visualize and preview the behavior of pmt. Every path through the graph created by pma (and drawn by pmg) is a trace (test run) that may be generated by pmt, when pma and pmt are invoked with the same arguments. There will be presentation on PyModel at Northwest Python Day 2010, on Saturday, Jan 30, in Seattle: http://www.seapig.org/NWPD10