title: Is it possible to set environment variables for exactly one test?
body: <p>Given something like this:</p>
  
  <pre><code>it('uses env variables correctly', function(done) {
      assert.equal(process.env.x * process.env.y, 10);
  });
  </code></pre>
  
  <p>I would like to set the <code>x</code> and <code>y</code> environment variable for this one test only. Is that possible?</p>