測試擴展到expect.js

Question

我正在寫一些expect.js匹配器，我想測試自己的匹配器。所以我想寫正面和負面的測試。假設我寫了

toContainItem(name); 

這樣使用;

expect(femaleNames).toContainItem('Brad'); // test fails 
expect(femaleNames).toContainItem('Angelina'); // test passes 

我想要做的是寫一個測試爲負的情況下，像這樣;

it('should fail if the item is not in the list', function() { 
    expect(function() { 
     expect(femaleNames).toContainItem('Brad'); 
    }).toFailTest('Could not find "Brad" in the array'); 
}); 

我不知道如何在一個環境中，它不會失敗的含試運行失敗我測試代碼。這可能嗎？

---

編輯：基於卡爾Manaster的答案，我想出了一個擴展期望，允許上面的代碼工作;

expect.extend({ 
    toFailTest(msg) { 
     let failed = false; 
     let actualMessage = ""; 
     try 
     { 
      this.actual(); 
     } 
     catch(ex) 
     { 
      actualMessage = ex.message; 
      failed = true; 
     } 

     expect.assert(failed, 'function should have failed exception'); 

     if(msg) { 
      expect.assert(actualMessage === msg, `failed test: expected "${msg}" but was "${actualMessage}"`); 
     } 
    } 
}); 

Answer 1

我想你可以包裝內期望在一個try/catch塊，在那裏你的catch子句中清除故障變量，然後做出關於變量的值，您的實際斷言。

let failed = true; 
try { 
    expect(femaleNames).toContainItem('Brad'); 
} catch (e) { 
    failed = false; 
} 
expected(failed).toBe(false);