What is the purpose of the output-expected folder?

[zzctmac]

Hi, I am using this fantastic tool to check my promise codes. But I am wondering what the purpose of the output-expected folder is.
For example, I have a code snippet:

function getFromApi(p) {
    return {'p': 1}
}
var performancePerMonth = new Promise(function(resolve, reject) {
    var path = some_path;
    getFromApi(path);
});

And I run this code snippet with the following setup:

function runTestsOnlyWithJalangi(testName){
    it(testName + '(runJalangi)', function (done) {                                 
        this.timeout(10000);
        common.runJalangi(testName, INPUT_DIR, ACTUAL_OUTPUT_DIR);
        done();
    });
}

I can get the promise graph, and it finds the unsettled promise:

In this process, I do not have an output-expected file to run with the following setup:

 it(testName + '(checkoutput)', function (done) {                              
        common.checkGeneratedCode(testName, ACTUAL_OUTPUT_DIR, EXPECTED_OUTPUT_DIR);
        done();
    });
    it(testName + 'checkGraph', function (done) {
        common.checkGeneratedGraph(testName, ACTUAL_OUTPUT_DIR, EXPECTED_OUTPUT_DIR);
        done();
    });

Hence, I would like to know the purpose of the output-expected folder. Is it necessary?