BDD Style Tests

test_adder.py

from decimal import Decimal as D
from numbers import Number

from django.test import TestCase


class Adder(object):
    def __init__(self, addend, augend):
        if not (isinstance(addend, Number) or isinstance(augend, Number)):
            raise TypeError('Adder requires both addend and augend to be Numbers.')

        self._addend = addend
        self._augend = augend

    def calculate(self):
        return self._addend + self._augend


class AdderTests(TestCase):
    def setUp(self):
        self.addend = 1
        self.augend = 2

    def test_add_integer_values(self):
        """ Should produce an integer with value equal to 3. """
        adder = Adder(int(self.addend), int(self.augend))
        result = adder.calculate()
        self.assertEquals(result, 3)
        self.assertIsInstance(result, int)

    def test_add_floating_point_values(self):
        """ Should produce a float with a value equal to 3.0. """
        adder = Adder(float(self.addend), float(self.augend))
        result = adder.calculate()
        self.assertEquals(result, 3.0)
        self.assertIsInstance(result, float)

    def test_add_complex_values(self):
        """ Should produce a complex with a value equal to 3+0j. """
        adder = Adder(complex(self.addend), complex(self.augend))
        result = adder.calculate()
        self.assertEquals(result, complex(3, 0))
        self.assertIsInstance(result, complex)

    def test_add_decimal_values(self):
        """ Should produce a decimal with a value equal to D('3.0'). """
        adder = Adder(D(self.addend), D(self.augend))
        result = adder.calculate()
        self.assertEquals(result, D('3.0'))
        self.assertIsInstance(result, D)

    def test_invalid_arguments(self):
        """ Should raise a TypeError when supplying non-numeric arguments. """
        with self.assertRaises(TypeError):
            Adder(None, None)