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本文为大致翻译以及操作实践。

测试驱动开发概念

测试驱动开发，也称为红绿重构，英文全称Test-Driven Development，简称TDD，是一种不同于传统软件开发流程的新型的开发方法。它要求在编写某个功能的代码之前先编写测试代码，然后只编写使测试通过的功能代码，通过测试来推动整个开发的进行。

测试驱动开发的五个步骤

• step1
  编写测试，编写功能代码前，先编写在满足功能规范时才能通过的测试开始
• step2
  运行测试，并确保它Fail，此时意味着你的测试生效（预期就是fail）
• step3
  编写最简单的代码，以便测试可以通过，但是不必在此步骤做的完美
• step4
  确保所有测试可以通过，包括旧的测试项，确保新功能符合规范，并且不会对其它东西造成破坏
• step5
  重构和改进代码

代码实例讲解

我们按照上述的五个步骤，依次讲解

step1：想实现一个支付员工工资的功能，先不实现这个功能，把大体结构写出来：

关于dataclass的用法，看我文章：每日Python小技巧–dataclass

"""
Very advanced Employee management system.
"""
from dataclasses import dataclass@dataclass
class Employee:"""Basic representation of an employee."""name: stremployee_id: intpay_rate: float = 100.0hours_worked: float = 0.0employer_cost: float = 1000.0has_commission: bool = Truecommission: float = 100.0contracts_landed: int = 0def compute_payout(self) -> float:"""Compute how much the employee should be paid."""raise NotImplementedError()

step2：编写测试并运行，此时运行应该都是失败的，因为功能没有实现：

"""
Employee class tests.
"""
import unittestfrom employee import EmployeeNAME: str = "Arjan"
EMPLOYEE_ID: int = 12345class TestEmployeeComputePayout(unittest.TestCase):"""Test the compute_payout method of the Employee class."""def setUp(self):"""Set up test fixtures."""self.arjan = Employee(name=NAME, employee_id=EMPLOYEE_ID)def test_employee_payout_returns_a_float(self):"""Whether payout returns a float."""self.assertIsInstance(self.arjan.compute_payout(), float)def test_employee_payout_no_commission_no_hours(self):"""Whether payout is correctly computed in case of no commission and no hours worked."""self.assertAlmostEqual(self.arjan.compute_payout(), 1000.0)def test_employee_payout_no_commission(self):"""Whether payout is correctly computed in case of no commission and 10 hours worked."""self.arjan.hours_worked = 10.0self.assertAlmostEqual(self.arjan.compute_payout(), 2000.0)def test_employee_payout_with_commission(self):"""Whether payout is correctly computed in case of10 contracts landed and 10 hours worked."""self.arjan.hours_worked = 10.0self.arjan.contracts_landed = 10self.assertAlmostEqual(self.arjan.compute_payout(), 3000.0)def test_employee_payout_commission_disabled(self):"""Whether payout is correctly computed in case of10 contracts landed and 10 hours worked,but commission is disabled."""self.arjan.hours_worked = 10.0self.arjan.contracts_landed = 10self.arjan.has_commission = Falseself.assertAlmostEqual(self.arjan.compute_payout(), 2000.0)if __name__ == "__main__":unittest.main()

step3：实现最基础的功能，部分case可以通过测试：

"""
Very advanced Employee management system.
"""
from dataclasses import dataclass@dataclass
class Employee:"""Basic representation of an employee."""name: stremployee_id: intpay_rate: float = 100.0hours_worked: float = 0.0employer_cost: float = 1000.0has_commission: bool = Truecommission: float = 100.0contracts_landed: int = 0def compute_payout(self) -> float:  # pass 1 fail 4"""Compute how much the employee should be paid."""payout = self.pay_rate * self.hours_workedreturn payout

step4：逐步完善：

    def compute_payout(self) -> float: # pass 4 fail 1"""Compute how much the employee should be paid."""payout = self.pay_rate * self.hours_worked + self.employer_costreturn payoutdef compute_payout(self) -> float: # pass 5 fail 0"""Compute how much the employee should be paid."""payout = self.pay_rate * self.hours_worked + self.employer_costif self.has_commission:payout += self.commission * self.contracts_landedreturn payout

step5：重构代码，此时我更改一些条件，修改相应的计算公式，那么所有的测试case都可以直接复用，高效准确：

注意和上面的差别：employer_cost这个费用，给改成了更细致的三项，但是测试结果依然是pass

"""
Very advanced Employee management system.
"""
from dataclasses import dataclass@dataclass
class Employee:"""Basic representation of an employee."""name: stremployee_id: intpay_rate: float = 100.0hours_worked: float = 0.0# employer_cost: float = 1000.0employer_office_costs: float = 200.0employer_401k_costs: float = 400.0employer_suppoer_costs: float = 400.0has_commission: bool = Truecommission: float = 100.0contracts_landed: int = 0def compute_payout(self) -> float:"""Compute how much the employee should be paid."""employer_cost = self.employer_office_costs + self.employer_401k_costs + self.employer_suppoer_costspayout = self.pay_rate * self.hours_worked + employer_costif self.has_commission:payout += self.commission * self.contracts_landedreturn payout