A quick-and-dirty Approval Testing tool for Python and Py.Test

approval.py

import string
import os
from filecmp import cmp as file_contents_equal


def _extension(template_file, format):
    if format is not None:
        return "." + format
    elif template_file is not None:
        return os.path.splitext(template_file)[1]
    else:
        return ".txt"

def approve(test_fn, template_file, format, args, kwargs):
    test_name = test_fn.__module__ + "." + test_fn.__name__
    extension = _extension(template_file, format)    
    received_file = test_name + "-received" + extension
    approved_file = test_name + "-approved" + extension
    
    with open(received_file, mode="w") as received:
        if template_file is None:
            test_fn(received, *args, **kwargs)
        else:
            template = string.Template(open(template_file).read())
            template_params = dict()
            template_params["_resourcedir"] = os.path.dirname(template_file);
            template_params.update(test_fn(*args, **kwargs))
            received.write(template.substitute(template_params))
    
    assert os.path.exists(approved_file), \
        "no approved file: " + approved_file
    assert file_contents_equal(received_file, approved_file), \
        "diff " + received_file + " " + approved_file
    
    os.remove(received_file)


def approval(template=None, format=None):
    def decorator(test_fn):
        def run_approval(*args, **kwargs):
            approve(test_fn, template, format, args, kwargs)
        return run_approval
    return decorator

example-template.md

Example

${x} + ${y} = ${sum}

example.py

from approval import approval

# Without a template, the test function is passed a stream and must write results to be approved
@approval(format="md")
def test_something(out):
    out.write("Example\n")
    out.write("=======\n")
    out.write("{} + {} = {}", 1, 2, 1+2)


# With a template, the test function must return a dict of template parameters that are expanded by the Python string.Template class
@approval(format="example-template.md")
def test_something_else():
    return dict(x: 1, y: 2, sum: 1+2)

# Either way, received and approved files will be written to / read from the current working directory.