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Learning Node.js for .NET Developers by Harry Cummings

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Creating test doubles

There are more tests we could write for the games service, but let's look at a different module for now. How would we go about testing our users middleware? The following code is from middleware/users.js:

module.exports = function(req, res, next) {
    let userId = req.cookies.userId;
    if (!userId) {
        userId = uuid.v4();
        res.cookie('userId', userId);
    }
    req.user = {
        id: userId
    };
    next();
};

In order to test this class, we will need to pass in arguments for the req, res, and next parameters with which our code interacts. We don't have a real request, response, or middleware pipeline available, so we need to create some stand-in values instead. Stand-in values such as this are generally called test doubles. Our code reads an attribute ...

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