node.js - Mocha、should.js 和断言异常

Question

我有一个文件app.coffee:

class TaskList

class Task
    constructor: (@name) ->
        @status = 'incomplete'
    complete: ->
        if @parent? and @parent.status isnt 'completed'
          throw "Dependent task '#{@parent.name}' is not completed."
        @status = 'complete'
        true
    dependsOn: (@parent) ->
        @parent.child = @
        @status = 'dependent'

# Prepare scope stuff
root = exports ? window
root.TaskList = TaskList
root.Task = Task

和一个名为 test/taskTest.coffee 的文件:

{TaskList, Task} = require '../app'
should = require 'should'

describe 'Task Instance', ->
    task1 = task2 = null
    it 'should have a name', ->
        something = 'asdf'
        something.should.equal 'asdf'
        task1 = new Task 'feed the cat'
        task1.name.should.equal 'feed the cat'
    it 'should be initially incomplete', ->
        task1.status.should.equal 'incomplete'
    it 'should be able to be completed', ->
        task1.complete().should.be.true
        task1.status.should.equal 'complete'
    it 'should be able to be dependent on another task', ->
        task1 = new Task 'wash dishes'
        task2 = new Task 'dry dishes'
        task2.dependsOn task1
        task2.status.should.equal 'dependent'
        task2.parent.should.equal task1
        task1.child.should.equal task2
    it 'should refuse completion it is dependent on an uncompleted task', ->
        (-> task2.complete()).should.throw "Dependent task 'wash dishes' is not completed."

如果我在终端中运行这个命令:mocha -r should --compilers coffee:coffee-script -R spec 我有一个失败的测试(最后一个)说它期待一个异常“附属任务‘洗碗’未完成。”但得到“未定义”。

如果我通过删除括号将 (-> task2.complete()).should.throw 更改为 -> task2.complete().should.throw，测试通过，如果我不抛出异常则失败。但是，如果我将异常消息更改为随机的内容，它仍然会通过。难道我做错了什么？如果消息字面上是“从属任务‘洗碗’未完成”，难道测试不应该通过吗？

Answer 1

您正在抛出一个字符串异常，而不是抛出一个错误对象。 throw() 寻找后者。所以如果你这样做，你的原始代码就可以工作:

throw new Error "Dependent task '#{@parent.name}' is not completed."

---

如果您在 CoffeeScript 中编写的内容产生了没有意义的结果，请尝试将其编译为 js(或将代码粘贴到 try CoffeeScript 中。您会看到:

-> task2.complete().should.throw "Dependent task 'wash dishes' is not completed."

编译为:

(function() {
  return task2.complete().should["throw"]("Dependent task 'wash dishes' is not completed.");
});

它只是定义了一个函数，并不执行它。这解释了为什么更改字符串没有区别。希望对您有所帮助。