Stub out the global craft() object for PHPUnit tests
Whew...this seems to do the trick!
Hopefully this is an appropriate way to handle things.

I created a new Craft class file in the 'tests' dir.  There I can stub out any \Craft\craft() methods the class under test depends on.

stub class \tests\Craft

&lt;?php

class Craft {

    public function __construct()
    {
    }

    public function jobs()
    {
        return 'xxx';
    }
    public function getJobs()
    {
        return 'xxx';
    }

    public function craft()
    {
        return $this;
    }
}


in the test class

&lt;?php

namespace Craft;

require_once '/www/craftcms/plugins/jobs/variables/JobsVariable.php';
require_once '/www/craftcms/tests/Craft.php';


class JobsVariableTest extends \PHPUnit_Framework_TestCase
{

    public function testJobs()
    {
        $jobs = new \Craft\JobsVariable();
        $this-&gt;assertEquals('xxx', $jobs-&gt;jobs());

    }
}
function craft()
{
    return new \Craft;
}


allows me to test this function...

public function jobs()
{
    return craft()-&gt;jobs();
}