The asynchronous nature of the Node platform means accounting for asynchronous behavior in the tests. Fortunately, the Node unit testing frameworks help in dealing with this, but it's worth spending a few moments considering the underlying problem.

Consider a code snippet like this, which you should save in a file named deleteFile.js:

var fs = require('fs');
exports.deleteFile = function(fname, callback) {
    fs.stat(fname, function(err, stats) {
        if (err)
            callback(new Error('the file '+fname+' does not exist'));
        else {
            fs.unlink(fname, function(err) {
                if (err)
        callback(new Error('Could not delete '+fname));
                else callback();
            });
        }
    });
}

The nature of the asynchronous code is that the execution order is nonlinear, even though the code is written linearly, meaning there is a complex relationship between time and the lines of code. This snippet, like many written with...