Javascript 如何使用 mocha.js 模拟用于单元测试的依赖类？
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How to mock dependency classes for unit testing with mocha.js?
提问by mvmoay
Given that I have two ES6 classes.
鉴于我有两个 ES6 类。
This is class A:
这是A类：
import B from 'B';
class A {
someFunction(){
var dependency = new B();
dependency.doSomething();
}
}
And class B:
B类：
class B{
doSomething(){
// does something
}
}
I am unit testing using mocha (with babel for ES6), chai and sinon, which works really great. But how can I provide a mock class for class B when testing class A?
我正在使用 mocha（ES6 的 babel）、chai 和 sinon 进行单元测试，效果非常好。但是，在测试 A 类时，如何为 B 类提供模拟类？
I want to mock the entire class B (or the needed function, doesn't actually matter) so that class A doesn't execute real code but I can provide testing functionality.
我想模拟整个 B 类（或所需的功能，实际上并不重要），以便 A 类不执行真正的代码，但我可以提供测试功能。
This is, what the mocha test looks like for now:
这就是 mocha 测试现在的样子：
var A = require('path/to/A.js');
describe("Class A", () => {
var InstanceOfA;
beforeEach(() => {
InstanceOfA = new A();
});
it('should call B', () => {
InstanceOfA.someFunction();
// How to test A.someFunction() without relying on B???
});
});
采纳答案by victorkohl
You can use SinonJS to create a stubto prevent the real function to be executed.
您可以使用 SinonJS 创建一个存根来阻止真正的函数被执行。
For example, given class A:
例如，给定 A 类：
import B from './b';
class A {
someFunction(){
var dependency = new B();
return dependency.doSomething();
}
}
export default A;
And class B:
B类：
class B {
doSomething(){
return 'real';
}
}
export default B;
The test could look like:
测试可能如下所示：
describe("Class A", () => {
var InstanceOfA;
beforeEach(() => {
InstanceOfA = new A();
});
it('should call B', () => {
sinon.stub(B.prototype, 'doSomething', () => 'mock');
let res = InstanceOfA.someFunction();
sinon.assert.calledOnce(B.prototype.doSomething);
res.should.equal('mock');
});
});
You can then restore the function if necessary using object.method.restore();:
如有必要，您可以使用object.method.restore();以下命令恢复该功能：
var stub = sinon.stub(object, "method");
Replaces object.method with a stub function. The original function can be restored by callingobject.method.restore();(orstub.restore();). An exception is thrown if the property is not already a function, to help avoid typos when stubbing methods.
var stub = sinon.stub(object, "method");
用存根函数替换 object.method。可以通过调用object.method.restore();(或stub.restore();)恢复原始功能 。如果该属性还不是函数，则会引发异常，以帮助避免在存根方法时出现拼写错误。
