Creating unit testing framework similar to Mocha JavaScript

Question

I'm working on creating a unit testing framework and I'm trying to figure out how the output is possible of the following section of code without the use of global variables:

describe("Test Title", function () {
    it("should return a string", function () {
        /* Assertions here */
    });
});
//OUTPUT: "PASS: Test Title should return a string"

Could someone explain how the it method call somehow manages to get one of its parameters up to describe ?

If that's not clear, what I'm trying to say is I would like to know how a variable can move through callbacks. If I understand what's happening, a method call to an outside function within a callback somehow gets an argument to another outside function.

Answer 1

You're probably thinking that it executes the callback passed to it. It doesn't. It just registers the callback as a test.

The simplest implementation is for describe to run tests:

var tests = [];

function describe(description,fn) {
    fn();
    for (var i=0;i<tests.length;i++) {
        try {
            tests[i].fn();
            console.log('FAIL:' + description + ' ' + tests[i].description);
        }
        catch (e) {
            console.log('FAIL:' + description + ' ' + tests[i].description);
        }
    }
}

function it(description,fn) {
    tests.push({
        description: description,
        fn: fn
    });
}

However, from glancing at the Mocha code it seems that even describe doesn't really run the code, only register the test suite for another function to process:

function describe(description,fn) {
    fn();
    testSuites.push({
        description: description,
        tests: tests.slice(0)
    });
}

But the logic is the same. Create a data structure with all the values and then process them.