Code Challenge #1 The Coin Calculator

We recently had interviews at work and gave each prospective employee a coding challenge. It is designed to make sure you are a competent programmer. With this being said our entire department decided to give it a go to see how we fared. Needless to say some did better than others.

Here is the challenge, the objective is simple, you have 30 minutes to write a class that will pass the following tests. The tests are currently in python but can be ported to any language you wish.

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from calculator import Calculator
import unittest

class TestCoinCalculator(unittest.TestCase):

    def setUp(self):
        self.calculator = Calculator()

    def test_using_int(self):
        self.assertEqual('1 * £20 note, 1 * £2 coin, 1 * £1 coin', self.calculator.calculate(23))

    def test_using_float(self):
        self.assertEqual('1 * £20 note, 1 * £2 coin, 1 * £1 coin, 1 * 10p coin, 1 * 2p coin, 1 * 1p coin',
                         self.calculator.calculate(23.13))

    def test_using_string(self):
        self.assertEqual('1 * £20 note, 1 * £2 coin, 1 * £1 coin', self.calculator.calculate('23'))

    def test_with_prefix(self):
        self.assertEqual('1 * £20 note, 1 * £2 coin, 1 * £1 coin', self.calculator.calculate('£23'))

    def test_with_suffix(self):
        self.assertEqual('1 * £20 note, 1 * £2 coin, 1 * £1 coin', self.calculator.calculate('£23.00p'))

    def test_multiple_notes(self):
        self.assertEqual('2 * £20 note', self.calculator.calculate('40'))

    def test_with_fractions(self):
        self.assertEqual('1 * £20 note, 1 * 10p coin, 1 * 2p coin, 1 * 1p coin', self.calculator.calculate('20.13'))

    def test_less_than_one(self):
        self.assertEqual('1 * 10p coin', self.calculator.calculate('0.10'))

    def test_complex_amount(self):
        self.assertEqual('3 * £20 note, 1 * £2 coin, 1 * £1 coin, 1 * 50p coin, 1 * 5p coin, 1 * 2p coin, 1 * 1p coin',
                         self.calculator.calculate(63.58))

if __name__ == '__main__':
    unittest.main()

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I will reveal what I managed to write in the comments later on.