Tests for https://github.com/enb-make/enb/blob/master/lib/preprocess/css-preprocessor.js#L51-L69

gistfile1.js

var css = [
        ["background: url('pic.png');", "background: url('../../common.blocks/pic/pic.png');"],
        ["background: #fff url('pic.png');", "background: #fff url('../../common.blocks/pic/pic.png');"],
        ["background: url('pic.png') #fff;", "background: url('../../common.blocks/pic/pic.png') #fff;"],
        ["background: url('http://ya.ru/pic.png');", "background: url('http://ya.ru/pic.png');"],
        ["background: url('//ya.ru/pic.png');", "background: url('//ya.ru/pic.png');"],
        ["background-image: url('pic.png');", "background-image: url('../../common.blocks/pic/pic.png');"],
        ["background: url('pic.png');background: url('pic.png');", "background: url('../../common.blocks/pic/pic.png');background: url('../../common.blocks/pic/pic.png');"],

        ["background: url(pic.png);", "background: url(../../common.blocks/pic/pic.png);"],
        ["background: #fff url(pic.png);", "background: #fff url(../../common.blocks/pic/pic.png);"],
        ["background: url(pic.png) #fff;", "background: url(../../common.blocks/pic/pic.png) #fff;"],
        ["background: url(http://ya.ru/pic.png);", "background: url(http://ya.ru/pic.png);"],
        ["background: url(//ya.ru/pic.png);", "background: url(//ya.ru/pic.png);"],
        ["background-image: url(pic.png);", "background-image: url(../../common.blocks/pic/pic.png);"],
        ["background: url(pic.png);background: url(pic.png);", "background: url(../../common.blocks/pic/pic.png);background: url(../../common.blocks/pic/pic.png);"],

        ["background-image: url('data:image/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20rl(%23l)20fill%3D%22none%22%2F%3E%3C%2Fsvg%3E');", "background-image: url('data:image/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20rl(%23l)20fill%3D%22none%22%2F%3E%3C%2Fsvg%3E');"],

    ],
    count = 0,
    CssPreprocessor = require('./lib/preprocess/css-preprocessor'),
    preprocessCss = new CssPreprocessor();

preprocessCss.setCssRelativeUrlBuilder(function(path) {
    return '../../common.blocks/pic/' + path;
});

css.forEach(function(item) {
    check(item[1], preprocessCss._processUrls(item[0], '../../common.blocks/pic/'));
    count++;
});
console.log('\033[32m%s tests passed\033[0m', count);

function check(expected, result) {
    console.assert(expected == result, '\nexpected: \033[31m' + expected, '\n\nresult: ' + result + '\033[0m')
}