How to use the node-red-node-test-helper.startServer function in node-red-node-test-helper

beforeEach(function(done) {
        fs.writeFileSync(fileToTail, "Tail message line 1\nTail message line 2\n");
        helper.startServer(done);
    });

beforeEach(function(done) {
            //fs.writeFileSync(fileToTest, "File message line 1\File message line 2\n");
            helper.startServer(done);
        });

beforeEach(function(done) {
        fs.existsSync(file).should.be.true;
        helper.startServer(done);
    });

startServer(function(err) {
            if (err) {
                done(err);
            }
            helper.startServer(done);
        });
    });

beforeEach(function(done) {
        if (testInterval !== null) {
            clearInterval(testInterval);
        }
        helper.startServer(done);
    });