Testing the output of JavaScript functions automatically

Question

I often test the output of JavaScript functions manually (by simply looking at the output of each function in the console), and this can often be quite tedious. In JavaScript, is there any way to test the output of a series of function calls automatically, and return all tests that did not produce the expected results?

checkOutput([["add(1, 2)", 3], ["add(2, 2)", 4]]); //if the input does not match the output in one of these arrays, then return the function call(s) that didn't produce the correct output

function checkOutput(functionArray){
    //this function is not yet implemented, and should return a list of function calls that did not produce correct output (if there are any).
}

function add(num1, num2){
    return num1 + num2;
}

Niet the Dark Absol · Accepted Answer · 2013-01-16 07:07:59Z

2

Seems as simple as looping, eval the first element of each array and compare it to the second.

function checkOutput(functionArray) {
    var check = function(e) {
        return eval(e[0]) !== e[1];
    };
    if( Array.prototype.filter)
        return functionArray.filter(check);
    // shim in older browsers
    var l = functionArray.length, i, out = [];
    for( i=0; i<l; i++)
        if( check(functionArray[i]))
            out.push(functionArray[i]);
    return out;
}

edited Jan 16, 2013 at 7:07

answered Jan 16, 2013 at 6:42

Niet the Dark Absol

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3 Comments

Anderson Green Over a year ago

There is a missing parentheses at this line: return eval(e[0]) !== e[1]);

Niet the Dark Absol Over a year ago

Thanks for pointing that out - I had originally written it as an if, then realised I was writing if (something) return true else return false

Anderson Green Over a year ago

Also, here is another automated testing method that I found: jsfiddle.net/jarble/S2wTJ

Ian Atkin · Accepted Answer · 2013-01-16 06:47:34Z

2

Absolutely. Use a Unit Testing suite, such as QUnit.

I like that one in particular, and it boasts that it's used by the various jQuery projects. That's a pretty solid endorsement.

A typical test would look something like this...

test( "add test", function(num1, num2) {
  ok( num1 + num2 == 42, "Passed!" );
});

And, if you don't like that suggestion, check out other Unit Testing frameworks at good ol' Wikipedia: JavaScript Unit Testing Frameworks.

edited Jan 16, 2013 at 6:47

answered Jan 16, 2013 at 6:41

Ian Atkin

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2 Comments

Anderson Green Over a year ago

Does QUnit do anything like this, by any chance? :)

Ian Atkin Over a year ago

Yes. As with any Unit Testing framework, you create assertions (expected == 1, etc.) and get results all at once.

twksos · Accepted Answer · 2013-01-16 06:41:44Z

1

Maybe you want switch to jasmine for testing javascript.

answered Jan 16, 2013 at 6:41

twksos

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Comments

Juho Vepsäläinen · Accepted Answer · 2013-01-16 06:52:47Z

My testing library, suite.js, does something like this. Basically the syntax looks like this:

suite(add, [
    [[1, 2]], 3
]);

Usually I bind a parameter using partial application so my tests look like this:

suite(partial(add, 1), [
    -5, 4,
    2, 3
]);

And taken to the ultimate level I skip these tests altogether and define a contract based on which I generate tests. For this I use annotate.js. In this case I would end up with something like the following:

// implementation
function adder(a, b) {
    return a + b;
}

var add = annotate('add', 'adds things').on(is.number, is.number, adder);

// test some invariants now
suite(add, function(op, a, b) {
    return op(a, b) == op(b, a);
});

I know it's not a trivial amount of code anymore. This allows you to define invariants for function parameters, though, and based on that information we can generate tests, documentation etc.

suite.js works only in Node environment for now but if there is enough interest, I don't mind porting it to browser so you can run your tests there.

keifer94 · Accepted Answer · 2013-01-16 06:42:50Z

0

Look into QUnit. You can basically run tests on your functions all at once.

answered Jan 16, 2013 at 6:42

keifer94

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