After stubbing function still it calls the real function

Question

I have stubbed the content of file, so I can run through only outer function

file.html

<body onload ="test('file.txt')">
<body>

file.js

    const fs1 = require('fs');
    let param;
    module.export = {
         test,
         test1,
         param
    }

    function test (outputParam) {
      let fileData = test1(outputParam);
      param = fileData;
    }

    function test1(outputParam) {
       let data = fs1.readFileSync(outputParam);
       return data; 
    }

Here as you see I load function test from html onload and in turn test1 calls and reads file, I have stubbed this file content as shown in the test below

When I run the test I want to see the variable param has the file content value

test.spec.js

    let sinon = require("sinon");
    let filejs = require('./file.js');

    it('should run only the outer function' ,function() {

    // I try to stub my function here
    sinon.stub(filejs,'test1').callsFake ((someArg) => {
      return "this is my file content";
    });

        // Now I will call my test function
        filejs.test(someArg);

    })

As you seen above I have stubbed function test1, still when I run the test I see test1 gets called and it reads the real file.

I am using mocha , I am new to stub or mock concepts, any suggestion is really appreciated.

sinon.stub() can only affect the properties of the export object but the test() function calls the internal function test1() directly. sinon.stub() can’t do anything about the internals of a module. — Lennholm

GOTO 0 GOTO 0 · Accepted Answer · 2020-02-19T10:39:34

You should probably try to stub readFileSync.

const fs = require('fs');

// ...

sinon.stub(fs, "readFileSync").callsFake ((someArg) => {
  return "this is my file content";
});

Besides that, I can spot two issues with your code.

The real readFileSync will return a Buffer if called without a second parameter, not a string like your stub does.
The body onload event only exists inside the DOM. The fs module is only available in Node.js. If you run your code in a browser, you won't be able to use fs.readFileSync. If you run it in Node, your HTML file and the onload event won't be useful.

After stubbing function still it calls the real function

1 Answers