[TIP] structure of a testing talk

[andrea crotti]

So now I thought that as a teaser example in the beginning of the talk
I will show a bad function, that does too many things:

import subprocess

import MySQLdb


def long_crappy_function():
    """Do a bit of everything
    """
    ls_cmd = 'ls'
    temp = '/tmp'
    p = subprocess.Popen(ls_cmd, stdout=subprocess.PIPE,
stderr=subprocess.PIPE, cwd=temp)

    out, err = p.communicate()
    res = []
    for line in out:
        if 'to-match' in line:
            res.append(line)

    dbc = MySQLdb.connect(host='host', user='user', passwd='passwd',
port='port')
    cursor = dbc.cursor(MySQLdb.cursors.DictCursor)

    for r in res:
       cursor.execute('INSERT INTO table VALUES (%s)' % r)


and in 4 iterative steps reach the following state:

import subprocess

import MySQLdb


def run_ls():
    ## launching a shell command
    ls_cmd = 'ls'
    temp = '/tmp'
    p = subprocess.Popen(ls_cmd, stdout=subprocess.PIPE,
stderr=subprocess.PIPE, cwd=temp)
    ## filtering the output of a shell command
    out, err = p.communicate()
    return out


def filter_output(out):
    res = []
    for line in out:
        if 'to-match' in line:
            res.append(line)

    return res


def update_to_database(res):
    ## updating the results to database
    dbc = MySQLdb.connect(host='host', user='user', passwd='passwd',
port='port')
    cursor = dbc.cursor(MySQLdb.cursors.DictCursor)

    for r in res:
       cursor.execute('INSERT INTO table VALUES (%s)' % r)


def main():
    """Update filtered result from a shell command to the database
    """
    out = run_ls()
    res = filter_output(out)
    update_to_database(res)


def test_filter_output():
    lines = ['x1: to-match', 'x2', 'x3: to-match..']
    desired = ['x1: to-match', 'x3: to-match..']
    assert filter_output(lines) == desired


if __name__ == '__main__':
    test_filter_output()


Where I have now a pure function and a st for it.

What do you think?  Another thing which would be nice is to do an
interactive group-solving example of TDD.

I propose a problem to solve, and together we start to write down the
specifications as tests, and make them pass one by one..

Any advice of a nice example to use?  I thought about managing
Rational numbers for example, but maybe it's a bit too abstract..