To fend off Microsoft, Yahoo is conducting a test with Google to have the latter broker ads for Yahoo's search results. The notion: Google will be so much more effective at selling ads than Yahoo that it will raise Yahoo's revenues, and therefore boost its value well beyond Microsoft's $44.6 billion offer. The test is supposedly "limited," covering only 3 percent of Yahoo's search traffic. But Mike Stoppelman, a former Google engineer, thinks that the deal may be more far-reaching than Yahoo or Google would like you to think.