Unit test helper for diffing Python data structures

gistfile1.py

def eq_diff(a, b):
    import json, difflib
    from datetime import datetime

    if a == b:
        return

    class DatetimeEncoder(json.JSONEncoder):
        def default(self, o):
            if isinstance(o, datetime):
                return o.isoformat()
            else:
                # Fall back to string
                return str(o)

    a_json = json.dumps(a, indent=4, sort_keys=True, cls=DatetimeEncoder)
    b_json = json.dumps(b, indent=4, sort_keys=True, cls=DatetimeEncoder)
    diff = ''.join(difflib.unified_diff(
        a_json.splitlines(True),
        b_json.splitlines(True),
        fromfile='actual',
        tofile='expected',
    ))
    raise AssertionError('\n' + diff)