如何在Jasmine中编写FileReader测试？

Question

我正在努力使这个测试工作,但我无法理解如何使用FileReader编写测试.这是我的代码

function Uploader(file) {
    this.file = file;
}

Uploader.prototype =  (function() {

    function upload_file(file, file_contents) {
        var file_data = new FormData()
        file_data.append('filename', file.name)
        file_data.append('mimetype', file.type)
        file_data.append('data', file_contents)
        file_data.append('size', file.size)

        $.ajax({
            url: "/upload/file",
            type: "POST",
            data: file_contents,            
            contentType: file.type,
            success: function(){

                // $("#thumbnail").attr("src", "/upload/thumbnail");    

            },
            error: function(){
                alert("Failed");
            },
            xhr: function() {
                myXhr = $.ajaxSettings.xhr();
                if(myXhr.upload){
                    myXhr.upload.addEventListener('progress',showProgress, false);
                } else {
                    console.log("Upload progress is not supported.");
                }
                return myXhr;
            }
        });
    }

    return {
        upload : function() {
            var self = this,
                reader = new FileReader(),
                file_content = {};

            reader.onload = function(e) {
                file_content = e.target.result.split(',')[1];

                upload_file(self.file, file_content);
            }
        }
    };
})();

这是我的考验

describe("Uploader", function() {
    it("should upload a file successfully", function() {
        spyOn($, "ajax");
        var fakeFile = {};

        var uploader = new Uploader(fakeFile);
        uploader.upload();

        expect($.ajax.mostRecentCall.args[0]["url"]).toEqual("/upload/file");
    })
});

但它永远不会到达reader.onload.

Answer 1

这里的问题reader.onload是难以测试的使用.您可以使用,reader.addEventListener以便您可以监视全局FileReader对象并返回模拟:

eventListener = jasmine.createSpy();
spyOn(window, "FileReader").andReturn({
 addEventListener: eventListener
})

那么你可以自己激活onload回调:

expect(eventListener.mostRecentCall.args[0]).toEqual('load');
eventListener.mostRecentCall.args[1]({
  target:{
    result:'the result you wanna test'
  }
})

Answer 2

此语法在2.0中已更改.下面的代码给出了一个基于AndreasKöberle答案但使用新语法的示例

    // create a mock object, its a function with some inspection methods attached
    var eventListener = jasmine.createSpy();

    // this is going to be returned when FileReader is instantiated
    var dummyFileReader = { addEventListener: eventListener };

    // pipe the dummy FileReader to the application when FileReader is called on window
    // this works because window.FileReader() is equivalent to new FileReader()
    spyOn(window, "FileReader").and.returnValue(dummyFileReader)

    // your application will do something like this ..
    var reader = new FileReader();

    // .. and attach the onload event handler
    reader.addEventListener('load', function(e) {

        // obviously this wouldnt be in your app - but it demonstrates that this is the 
        // function called by the last line - onloadHandler(event);
        expect(e.target.result).toEqual('url');

        // jasmine async callback
        done();
    });

    // if addEventListener was called on the spy then mostRecent() will be an object. 
    // if not it will be null so careful with that. the args array contains the 
    // arguments that addEventListener was called with. in our case arg[0] is the event name ..
    expect(eventListener.calls.mostRecent().args[0]).toEqual('load');

    // .. and arg[1] is the event handler function
    var onloadHandler = eventListener.calls.mostRecent().args[1];

    // which means we can make a dummy event object .. 
    var event = { target : { result : 'url' } };

    // .. and call the applications event handler with our test data as if the user had 
    // chosen a file via the picker
    onloadHandler(event);

Answer 3

我也遇到了类似的问题，并且能够在不使用 addeventlistener 的情况下实现它。我使用过onloadend，所以下面是我所做的。我的 ts 文件有以下代码：-

    let reader = new FileReader();
    reader.onloadend = function() {
                let dataUrl = reader.result;
                // Some working here
            };
    reader.readAsDataURL(blob);

我的规范文件（测试）案例代码：-

 let mockFileReader = {
            result:'',
            readAsDataURL:(blobInput)=> {
                console.log('readAsDataURL');
            },
            onloadend:()=> {
                console.log('onloadend');
            }
        };

    spyOn<any>(window, 'FileReader').and.returnValue(mockFileReader);
    spyOn<any>(mockFileReader, 'readAsDataURL').and.callFake((blobInput)=> {
        // debug your running application and assign to "encodedString" whatever 
        //value comes actually after using readAsDataURL for e.g. 
        //"data:*/*;base64,XoteIKsldk......"
        mockFileReader.result = encodedString;
        mockFileReader.onloadend();
    });

通过这种方式，您模拟了 FileReader 对象并返回了对您自己的“readAsDataURL”的虚假调用。因此，现在当您的实际代码调用“reasAsDataURL”时，您的假函数将被调用，您将在“result”中分配一个编码字符串并调用“onloadend”函数，该函数已经在您的代码 (.ts) 文件中分配了一个功能。因此它以预期的结果被调用。希望能帮助到你。