测试扩展到expect.js

Question

我正在写一些expect.js匹配器，我想测试自己的匹配器。所以我想写正面和负面的测试。假设我写了

toContainItem(name); 

这样使用;

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

我想要做的是写一个测试为负的情况下，像这样;

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'); 
}); 

我不知道如何在一个环境中，它不会失败的含试运行失败我测试代码。这可能吗？

---

编辑：基于卡尔Manaster的答案，我想出了一个扩展期望，允许上面的代码工作;

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

我想你可以包装内期望在一个try/catch块，在那里你的catch子句中清除故障变量，然后做出关于变量的值，您的实际断言。

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