問題描述

expect(something).toBe(true)、expect(something).toBeTruthy()和expect(something).toBeTrue有什么區別()?

請注意，toBeTrue() 是 中引入的自定義匹配器>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().

這個問題是通用的，但是，作為一個真實的例子，我正在測試一個元素是否顯示在 protractor 中.在這種情況下我應該使用哪個匹配器?

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();

推薦答案

當我想知道類似這里提出的問題時，我會做的是去源頭.

What I do when I wonder something like the question asked here is go to the source.

expect().toBe() 定義為:

function toBe() {
  return {
    compare: function(actual, expected) {
      return {
        pass: actual === expected
      };
    }
  };
}

它使用 === 執行測試，這意味著當用作 expect(foo).toBe(true) 時，只有在 foo 實際上的值為 true.真實值不會使測試通過.

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() 定義為:

function toBeTruthy() {
  return {
    compare: function(actual) {
      return {
        pass: !!actual
      };
    }
  };
}

類型強制

如果將該值強制轉換為布爾值，則該值是真值 true.!! 操作通過將傳遞給 expect 的值強制為布爾值來測試真實性.請注意，與當前接受的答案暗示相反，== true 不是 真實性的正確測試.你會得到一些有趣的東西，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 !! 會產生:

> !!"hello"
true
> !!""
false
> !![1, 2, 3]
true
> !![] 
true

(是的，無論是否為空，數組都是真實的.)

(Yes, empty or not, an array is truthy.)

expect().toBeTrue() 是 Jasmine-Matchers 的一部分a> (在后來的項目首先注冊 jasmine-matchers 后，在 npm 上注冊為 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() 定義為:

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

expect().toBeTrue()和expect().toBe(true)的區別在于expect().toBeTrue()code> 測試它是否在處理 Boolean 對象.expect(new Boolean(true)).toBe(true) 會失敗，而 expect(new Boolean(true)).toBeTrue() 會通過.這是因為這個有趣的事情:

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

至少它是真實的:

> !!new Boolean(true)
true

哪個最適合與 elem.isDisplayed() 一起使用?

最終 Protractor 將此請求交給 Selenium.documentation 聲明 產生的值.isDisplayed() 是一個解析為 boolean 的承諾.我會從表面上看它并使用 .toBeTrue() 或 .toBe(true).如果我發現實現返回真值/假值的情況，我會提交錯誤報告.

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.

這篇關于toBe(true) vs toBeTruthy() vs toBeTrue()的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！