NodeUnit testing mysql function test always successful - node.js

Question

I'm trying to learn how to use NodeUnit to test my NodeJs code. Ive written the following code, however each time I run the test, the result is OK: 0 assertions, no matter whether the input parameter is valid or not. Can anyone explain why this doesn't work and how I can fix it?
auth.class.js: This function accepts a user ID and returns a username.
exports.username = function(uid, callback) {
db.query('SELECT username FROM ul_logins WHERE id=?', uid, function(err, results){
if (err) throw new Error(err);
if(results.length > 0)
{
callback(null, results[0].username);
}
else
throw new Error("No results.");
});
};
authtest.js: This test will run successful every time, no matter what the uid is, and count 0 assertions.
var auth = require('./auth.class.js');
exports['username'] = function (test) {
auth.username(1, function(err, data){
return test.equal(data, "joe#example.com");
});
test.done();
};

Answer 1

The function you are testing is asynchronous (see the rewritten function below). You need to put the test.done() in the callback function:
exports['username'] = function (test) {
test.expect(2);
auth.username(1, function (err, data) {
test.ifError(err);
test.equal(data, 'joe#example.com');
test.done();
});
};
In your version, test.done gets called before the callback to auth.username is called. Use test.expect to tell nodeunit how many asserts it should receive before test.done is called.
You have a serious problem in your auth.username function. You should not throw in asynchronous code since a try-catch cannot be used to catch the error, leading to uncaught exceptions. You should always pass errors in asynchronous code to a callback as the first argument (convention). Your function should look like:
exports.username = function (uid, callback) {
var query = 'SELECT username FROM ul_logins WHERE id=?';
db.query(query, uid, function (err, results) {
if (err) {
return callback(err);
}
if (results.length === 0) {
return callback(new Error('No user found.'));
}
callback(null, results[0].username);
});
};
Note that errors are handled first (keeps the code neat), and callback calls in the branches are returned to avoid calling the callback multiple times (using else adds a level of indentation).
I get the impression that you are new to Node, and I remember having difficulty over this point too. Consider any function that does something over the network as asynchronous. This could take a long time, so to avoid blocking the process Node gets the OS to handle the task, and takes a callback to call at some point in the future when the OS gives it a result. This is why Node relies so heavily on callbacks. It leaves the Node process free to do other things (like call test.done in your question) while it waits. It also means that try-catch (which can only catch errors thrown in the same 'tick') no longer works. The conventional way to handle errors is to call the callback with the error as the first argument. All other arguments are for actual results.