test_builder.py

from unittest import TestCase

class Field:
    def __init__(self, name, value):
        self.value = value
        self.name = name

    def __str__(self):
        return 'self.%s = %s' % (self.name, self.value)


class Class:
    def __init__(self, name):
        self.name = name
        self.fields = []

    def __str__(self):
        lines = ['class %s:' % self.name]
        if not self.fields:
            lines.append('  pass')
        else:
            lines.append('  def __init__(self):')
            for f in self.fields:
                lines.append('    %s' % f)
        return '\n'.join(lines)


class CodeBuilder:
    def __init__(self, root_name):
        self.__class = Class(root_name)

    def add_field(self, type, name):
        self.__class.fields.append(Field(type, name))
        return self

    def __str__(self):
        return self.__class.__str__()


class Evaluate(TestCase):
    @staticmethod
    def preprocess(s=''):
        return s.strip().replace('\r\n', '\n')

    def test_empty(self):
        cb = CodeBuilder('Foo')
        self.assertEqual(
            self.preprocess(str(cb)),
            'class Foo:\n  pass'
        )

    def test_person(self):
        cb = CodeBuilder('Person').add_field('name', '""') \
            .add_field('age', 0)
        self.assertEqual(self.preprocess(str(cb)),
                         """class Person:
  def __init__(self):
    self.name = \"\"
    self.age = 0""")