Sorry I have some more:

    assert.equal(resolve('..//index.js', './dir/c.js'), './/index.js');
    assert.equal(resolve('../../gre/modules/XPCOMUtils.jsm', 'resource://thing/utils/file.js', 'resource://thing/gre/modules/XPCOMUtils.jsm');
    assert.equal(resolve('../../gre/modules/XPCOMUtils.jsm', 'chrome://thing/utils/file.js', 'resource://thing/gre/modules/XPCOMUtils.jsm');
    assert.equal(resolve('../../a/b/c.json', 'file:///thing/utils/file.js', 'file:///thing/utils/a/b/c.json');