我如何在要尝试开玩笑的类中模拟私有属性

debugcn 发表于 Dev

克里斯·施密茨

我有一个要测试的类方法：

setStepResolution(resolution: stepResolution): void {
        switch (resolution) {
            case stepResolution.FULL_SETUP:
                this.stepperMotors.left.ms1Pin.digitalWrite(0)
                this.stepperMotors.left.ms2Pin.digitalWrite(0)
                this.stepperMotors.left.ms3Pin.digitalWrite(1)
                this.stepperMotors.right.ms1Pin.digitalWrite(0)
                this.stepperMotors.right.ms2Pin.digitalWrite(0)
                this.stepperMotors.right.ms3Pin.digitalWrite(1)
                break
            case stepResolution.HALF_STEP:
                this.stepperMotors.left.ms1Pin.digitalWrite(1)
                this.stepperMotors.left.ms2Pin.digitalWrite(0)
                this.stepperMotors.left.ms3Pin.digitalWrite(0)
                this.stepperMotors.right.ms1Pin.digitalWrite(1)
                this.stepperMotors.right.ms2Pin.digitalWrite(0)
                this.stepperMotors.right.ms3Pin.digitalWrite(0)
                break

这些digitalWrite调用中的每一个都针对在构造我的类时创建的不同类的实例：

export default class BotController {

    private stepperMotors: StepperMotorCollection

    constructor() {
        this.initalizeMotors()
    }

    private initalizeMotors(): void {
        this.stepperMotors = {
            left: {
                directionPin: new Gpio(Number(process.env.LEFT_DIRECTION_PIN), { mode: Gpio.OUTPUT }),
                stepPin: new Gpio(Number(process.env.LEFT_STEP_PIN), { mode: Gpio.OUTPUT }),
                ms1Pin: new Gpio(Number(process.env.LEFT_RESOLUTION_PIN_MS1), { mode: Gpio.OUTPUT }),
                ms2Pin: new Gpio(Number(process.env.LEFT_RESOLUTION_PIN_MS2), { mode: Gpio.OUTPUT }),
                ms3Pin: new Gpio(Number(process.env.LEFT_RESOLUTION_PIN_MS3), { mode: Gpio.OUTPUT }),
                stepsPerMM: Number(process.env.LEFT_STEPS_PER_MM),
                swapCoils: Boolean(process.env.LEFT_SWAP_COILS),
            },
            right: {
                directionPin: new Gpio(Number(process.env.RIGHT_DIRECTION_PIN), { mode: Gpio.OUTPUT }),
                stepPin: new Gpio(Number(process.env.RIGHT_STEP_PIN), { mode: Gpio.OUTPUT }),
                ms1Pin: new Gpio(Number(process.env.RIGHT_RESOLUTION_PIN_MS1), { mode: Gpio.OUTPUT }),
                ms2Pin: new Gpio(Number(process.env.RIGHT_RESOLUTION_PIN_MS2), { mode: Gpio.OUTPUT }),
                ms3Pin: new Gpio(Number(process.env.RIGHT_RESOLUTION_PIN_MS3), { mode: Gpio.OUTPUT }),
                stepsPerMM: Number(process.env.RIGHT_STEPS_PER_MM),
                swapCoils: Boolean(process.env.RIGHT_SWAP_COILS),
            },
        }
    }

我可以使用类的模拟stepperMotors在测试中为属性创建模拟Gpio（我已经在模拟其他一些测试的构造函数）：

test("can change step resolution", () => {
        // * The step resolution of the stepper motors can be changed via the code.
        // * The settings can be controlled by an enum that denotes each of the possible
        // * resolutions.

        const mockStepperMotorConfiguration: StepperMotorCollection = {
            left: {
                directionPin: new pigpio.Gpio(1),
                stepPin: new pigpio.Gpio(1),
                ms1Pin: new pigpio.Gpio(1),
                ms2Pin: new pigpio.Gpio(1),
                ms3Pin: new pigpio.Gpio(1),
                stepsPerMM: 1,
                swapCoils: false,
            },
            right: {
                directionPin: new pigpio.Gpio(1),
                stepPin: new pigpio.Gpio(1),
                ms1Pin: new pigpio.Gpio(1),
                ms2Pin: new pigpio.Gpio(1),
                ms3Pin: new pigpio.Gpio(1),
                stepsPerMM: 1,
                swapCoils: false,
            },
        }

        // ^ To change the resolution to a full step
        // * send in the full step enum
        newController.setStepResolution(stepResolution.FULL_SETUP)

但是我不能，因为stepperMotor财产是私有的。

有几种方法可以解决此问题（将属性设置为公共，设置属性的设置为公共方法），但似乎都不可行，因为该属性永远不能在类外部访问，因此我只公开了属性或方法支持测试。

还有另一种进行这种测试的方法吗？我知道开玩笑我可以通过替换原型函数来模拟javascript类中的方法，例如：

BotController.prototype.someMethod = jest.fn()
const controller = new BotController

如果这是我要模拟的类，则可以将属性作为模拟实现传递，例如：

jest.mock("../BotController", () => ({
    stepperMotors: mockStepperMotorConfiguration
}))

但是随后，该类中的其他所有内容也将被嘲笑，您将失去这一点。

对我应该如何处理这个有任何想法吗？

更新：尝试创建后门

我正在尝试Taplar创建后门的方法。

我尝试将控制器实例转换为any：

But the complier is still yelling at me:

Another update

After Taplar pointed out how to call the method on the cast version the errors went away on the back door which is fantastic!

The next wall I smashed into was that now for some reason the test can't see my mock anymore which is weird because the variable is local to the test.

Estus Flask

Unless # hard privacy is used, private properties can be accessed outside a class at runtime, TypeScript access modifiers are applied only at compilation time.

Accessing private members in tests can be considered a reflection.

Visibility can be bypassed with bracket notation, which is the preferable option:

controllerInstance['stepperMotors'] = ...;

Or with Reflect API:

Reflect.set(controllerInstance, 'stepperMotors', ...);

Or by disabling type checks:

(controllerInstance as any).stepperMotors = ...;

由于私有属性是通过原型方法设置的，因此另一种方法是对其进行模拟。如果原始初始化导致不良副作用并需要避免，则适用。BotController.prototype.someMethod = jest.fn()切勿在Jest中使用它，因为它无法自动清理并交叉污染测试。相反，它可能是：

jest.spyOn(BotController.prototype, 'initalizeMotors').mockImplementation(function (this: BotController) {
  this['stepperMotors'] = ...;
});
...
expect(controllerInstance['initalizeMotors']).toHaveBeenCalled();

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编辑于2021-04-5

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