toBe(true) vs toBeTruthy() vs toBeTrue()-前端问题

toBe(true) vs toBeTruthy() vs toBeTrue()(toBe(true) vs toBeTruthy() vs toBeTrue())

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问题描述

expect(something).toBe(true)、expect(something).toBeTruthy()和expect(something).toBeTrue有什么区别()?


请注意，toBeTrue() 是  中引入的自定义匹配器>jasmine-matchers 以及其他有用且方便的匹配器，例如 toHaveMethod() 或 toBeArrayOfStrings().
Note that toBeTrue() is a custom matcher introduced in jasmine-matchers among other useful and handy matchers like toHaveMethod() or toBeArrayOfStrings().
这个问题是通用的，但是，作为一个真实的例子，我正在测试一个元素是否显示在 protractor 中.在这种情况下我应该使用哪个匹配器?
The question is meant to be generic, but, as a real-world example, I'm testing that an element is displayed in protractor. Which matcher should I use in this case?
expect(elm.isDisplayed()).toBe(true);
expect(elm.isDisplayed()).toBeTruthy();
expect(elm.isDisplayed()).toBeTrue();


推荐答案
当我想知道类似这里提出的问题时，我会做的是去源头.
What I do when I wonder something like the question asked here is go to the source.
expect().toBe() 定义为:
function toBe() {
  return {
    compare: function(actual, expected) {
      return {
        pass: actual === expected
      };
    }
  };
}

它使用 === 执行测试，这意味着当用作 expect(foo).toBe(true) 时，只有在 foo 实际上的值为 true.真实值不会使测试通过.
It performs its test with === which means that when used as expect(foo).toBe(true), it will pass only if foo actually has the value true. Truthy values won't make the test pass.
expect().toBeTruthy() 定义为:
function toBeTruthy() {
  return {
    compare: function(actual) {
      return {
        pass: !!actual
      };
    }
  };
}

类型强制
如果将该值强制转换为布尔值，则该值是真值 true.!! 操作通过将传递给 expect 的值强制为布尔值来测试真实性.请注意，与当前接受的答案暗示相反，== true 不是 真实性的正确测试.你会得到一些有趣的东西，比如


Type coercion

A value is truthy if the coercion of this value to a boolean yields the value true. The operation !! tests for truthiness by coercing the value passed to expect to a boolean. Note that contrarily to what the currently accepted answer implies, == true is not a correct test for truthiness. You'll get funny things like 
> "hello" == true
false
> "" == true
false
> [] == true
false
> [1, 2, 3] == true
false

而使用 !! 会产生:
> !!"hello"
true
> !!""
false
> !![1, 2, 3]
true
> !![] 
true

(是的，无论是否为空，数组都是真实的.)
(Yes, empty or not, an array is truthy.)

expect().toBeTrue() 是 Jasmine-Matchers 的一部分a> (在后来的项目首先注册 jasmine-matchers 后，在 npm 上注册为 jasmine-expect).

expect().toBeTrue() is part of Jasmine-Matchers (which is registered on npm as jasmine-expect after a later project registered jasmine-matchers first).

expect().toBeTrue() 定义为:

function toBeTrue(actual) {
  return actual === true ||
    is(actual, 'Boolean') &&
    actual.valueOf();
}

expect().toBeTrue()和expect().toBe(true)的区别在于expect().toBeTrue()code> 测试它是否在处理 Boolean 对象.expect(new Boolean(true)).toBe(true) 会失败，而 expect(new Boolean(true)).toBeTrue() 会通过.这是因为这个有趣的事情:

The difference with expect().toBeTrue() and expect().toBe(true) is that expect().toBeTrue() tests whether it is dealing with a Boolean object. expect(new Boolean(true)).toBe(true) would fail whereas expect(new Boolean(true)).toBeTrue() would pass. This is because of this funny thing:

> new Boolean(true) === true
false
> new Boolean(true) === false
false

至少它是真实的:

> !!new Boolean(true)
true

哪个最适合与 `elem.isDisplayed()` 一起使用?

最终 Protractor 将此请求交给 Selenium.documentation 声明 产生的值.isDisplayed() 是一个解析为 boolean 的承诺.我会从表面上看它并使用 .toBeTrue() 或 .toBe(true).如果我发现实现返回真值/假值的情况，我会提交错误报告.

Which is best suited for use with `elem.isDisplayed()`?

Ultimately Protractor hands off this request to Selenium. The documentation states that the value produced by .isDisplayed() is a promise that resolves to a boolean. I would take it at face value and use .toBeTrue() or .toBe(true). If I found a case where the implementation returns truthy/falsy values, I would file a bug report.

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