由于大多数开发人员不建议测试私有函数，为什么不测试它呢?

Eg.

YourClass.ts

export class FooBar {
  private _status: number;

  constructor( private foo : Bar ) {
    this.initFooBar({});
  }

  private initFooBar(data){
    this.foo.bar( data );
    this._status = this.foo.foo();
  }
}

TestYourClass.spec.ts

describe("Testing foo bar for status being set", function() {

...

//Variable with type any
let fooBar;

fooBar = new FooBar();

...
//Method 1
//Now this will be visible
fooBar.initFooBar();

//Method 2
//This doesn't require variable with any type
fooBar['initFooBar'](); 
...
}

感谢@Aaron， @Thierry Templier。

“不要测试私有方法”的重点实际上是像使用它的人那样测试类。

如果你有一个带有5个方法的公共API，你的类的任何消费者都可以使用这些方法，因此你应该测试它们。使用者不应该访问类的私有方法/属性，这意味着在公共公开功能保持不变的情况下，可以更改私有成员。

如果依赖内部可扩展功能，请使用protected而不是private。 注意protected仍然是一个公共API(!)，只是使用方式不同。

class OverlyComplicatedCalculator {
    public add(...numbers: number[]): number {
        return this.calculate((a, b) => a + b, numbers);
    }
    // can't be used or tested via ".calculate()", but it is still part of your public API!
    protected calculate(operation, operands) {
        let result = operands[0];
        for (let i = 1; i < operands.length; operands++) {
            result = operation(result, operands[i]);
        }
        return result;
    }
}

单元测试保护的属性与消费者使用它们的方式相同，通过子类化:

it('should be extensible via calculate()', () => {
    class TestCalculator extends OverlyComplicatedCalculator {
        public testWithArrays(array: any[]): any[] {
            const concat = (a, b) => [].concat(a, b);
            // tests the protected method
            return this.calculate(concat, array);
        }
    }
    let testCalc = new TestCalculator();
    let result = testCalc.testWithArrays([1, 'two', 3]);
    expect(result).toEqual([1, 'two', 3]);
});

我同意@toskv的观点:我不建议这么做:-)

但是如果你真的想测试你的私有方法，你可以意识到TypeScript的相应代码对应于构造函数原型的一个方法。这意味着它可以在运行时使用(然而您可能会有一些编译错误)。

例如:

export class FooBar {
  private _status: number;

  constructor( private foo : Bar ) {
    this.initFooBar({});
  }

  private initFooBar(data){
    this.foo.bar( data );
    this._status = this.foo.foo();
  }
}

将转化为:

(function(System) {(function(__moduleName){System.register([], function(exports_1, context_1) {
  "use strict";
  var __moduleName = context_1 && context_1.id;
  var FooBar;
  return {
    setters:[],
    execute: function() {
      FooBar = (function () {
        function FooBar(foo) {
          this.foo = foo;
          this.initFooBar({});
        }
        FooBar.prototype.initFooBar = function (data) {
          this.foo.bar(data);
          this._status = this.foo.foo();
        };
        return FooBar;
      }());
      exports_1("FooBar", FooBar);
    }
  }
})(System);

查看这个plunkr: https://plnkr.co/edit/calJCF?p=preview。

我同意你的观点，尽管“只对公共API进行单元测试”是一个很好的目标，但有时它看起来并不那么简单，你会觉得你在API和单元测试之间做出选择。你已经知道了，因为这正是你想要做的，所以我就不多说了。:)

在TypeScript中，我发现了一些为了单元测试而访问私有成员的方法。考虑这个类:

class MyThing {

    private _name:string;
    private _count:number;

    constructor() {
        this.init("Test", 123);
    }

    private init(name:string, count:number){
        this._name = name;
        this._count = count;
    }

    public get name(){ return this._name; }

    public get count(){ return this._count; }

}

尽管TS使用private、protected、public来限制对类成员的访问，但编译后的JS没有private成员，因为这在JS中是不存在的。它纯粹用于TS编译器。因此:

You can assert to any and escape the compiler from warning you about access restrictions: (thing as any)._name = "Unit Test"; (thing as any)._count = 123; (thing as any).init("Unit Test", 123); The problem with this approach is that the compiler simply has no idea what you are doing right of the any, so you don't get desired type errors: (thing as any)._name = 123; // wrong, but no error (thing as any)._count = "Unit Test"; // wrong, but no error (thing as any).init(0, "123"); // wrong, but no error This will obviously make refactoring more difficult. You can use array access ([]) to get at the private members: thing["_name"] = "Unit Test"; thing["_count"] = 123; thing["init"]("Unit Test", 123); While it looks funky, TSC will actually validate the types as if you accessed them directly: thing["_name"] = 123; // type error thing["_count"] = "Unit Test"; // type error thing["init"](0, "123"); // argument error To be honest I don't know why this works. This is apparently an intentional "escape hatch" to give you access to private members without losing type safety. This is exactly what I think you want for your unit-testing.

下面是TypeScript Playground中的一个工作示例。

编辑为TypeScript 2.6

另一个选项是使用// @ts-ignore(在TS 2.6中添加)，它简单地抑制了下面一行的所有错误:

// @ts-ignore
thing._name = "Unit Test";

这样做的问题是，它抑制了下面一行的所有错误:

// @ts-ignore
thing._name(123).this.should.NOT.beAllowed("but it is") = window / {};

我个人认为@ts-ignore是一种代码气味，正如文档所说:

我们建议您尽量少使用这些注释。(强调原创)

很抱歉在这篇文章中出现了死灵，但我觉得有必要对一些似乎没有涉及到的事情进行权衡。

First a foremost - when we find ourselves needing access to private members on a class during unit testing, it is generally a big, fat red flag that we've goofed in our strategic or tactical approach and have inadvertently violated the single responsibility principal by pushing behavior where it does not belong. Feeling the need to access methods that are really nothing more than an isolated subroutine of a construction procedure is one of the most common occurrences of this; however, it's kind of like your boss expecting you to show up for work ready-to-go and also having some perverse need to know what morning routine you went through to get you into that state...

发生这种情况的另一个最常见的实例是当您发现自己试图测试众所周知的“神类”时。这本身是一种特殊的问题，但同样的基本问题是需要知道手术的详细信息——但这就跑题了。

在这个特定的例子中，我们有效地将完全初始化Bar对象的责任分配给了FooBar类的构造函数。在面向对象编程中，一个核心原则是构造函数是“神圣的”，应该防范无效数据，这些无效数据会使构造函数自己的内部状态失效，并使它在下游的其他地方(可能是一个非常深的管道)失败。

在这里，我们没有做到这一点，因为我们允许FooBar对象接受一个在构造FooBar时还没有准备好的Bar，并通过某种“hack”FooBar对象来补偿它，让它自己来处理问题。

This is the result of a failure to adhere to another tenent of object oriented programming (in the case of Bar,) which is that an object's state should be fully initialized and ready to handle any incoming calls to its' public members immediately after creation. Now, this does not mean immediately after the constructor is called in all instances. When you have an object that has many complex construction scenarios, then it is better to expose setters to its optional members to an object that is implemented in accordance with a creation design-pattern (Factory, Builder, etc...) In any of the latter cases, you would be pushing the initialization of the target object off into another object graph whose sole purpose is directing traffic to get you to a point where you have a valid instance of that which you are requesting - and the product should not be considered "ready" until after this creation object has served it up.

在你的例子中，Bar的“status”属性似乎不在一个FooBar可以接受的有效状态中——所以FooBar对它做了一些事情来纠正这个问题。

The second issue I am seeing is that it appears that you are trying to test your code rather than practice test-driven development. This is definitely my own opinion at this point in time; but, this type of testing is really an anti-pattern. What you end up doing is falling into the trap of realizing that you have core design problems that prevent your code from being testable after the fact, rather than writing the tests you need and subsequently programming to the tests. Either way you come at the problem, you should still end up with the same number of tests and lines of code had you truly achieved a SOLID implementation. So - why try and reverse engineer your way into testable code when you can just address the matter at the onset of your development efforts?

如果您这样做了，那么您将更早地意识到，为了测试您的设计，您将不得不编写一些相当繁琐的代码，并且将有机会在早期通过将行为转移到易于测试的实现来重新调整您的方法。

Aaron的答案是最好的，对我来说也很有用:) 我会给它投票，但遗憾的是我不能(失去声誉)。

我不得不说，测试私有方法是使用它们并在另一方面有干净代码的唯一方法。

例如:

class Something {
  save(){
    const data = this.getAllUserData()
    if (this.validate(data))
      this.sendRequest(data)
  }
  private getAllUserData () {...}
  private validate(data) {...}
  private sendRequest(data) {...}
}

不一次测试所有这些方法是很有意义的，因为我们需要模拟出那些私有方法，我们不能模拟出来，因为我们不能访问它们。这意味着我们需要对一个单元测试进行大量的配置，以将其作为一个整体进行测试。

这就是说，测试上述方法的所有依赖关系的最佳方法是端到端测试，因为这里需要集成测试，但如果您正在实践TDD(测试驱动开发)，则端到端测试对您没有帮助，但测试任何方法都有帮助。