AdMob TEST_EMULATOR doesn't work alone

AdMob TEST_EMULATOR doesn't work alone

I'm trying to implement AdMob banners on an Android app.
Even if I'm using
adRequest.addTestDevice(AdRequest.TEST_EMULATOR);
in my code to run test banners in emulator, I still get the real banners.
Also LogCat is showing the message:
I/Ads(2364): To get test ads on this device, call
adRequest.addTestDevice("94**************************B664");
What's strange is the fact that the Device ID number has changed 3 times
today. I wasn't able to find how and when changed. So using those ID
numbers in my code, I can run test banners, until the number will change
again.
adRequest.addTestDevices(AdRequest.TEST_EMULATOR);
adRequest.addTestDevice("94**************************B664"); // My Eclipse
I have no Android device connected to my computer. All tests was done on
Eclipse.
Please help me to understand this. Why TEST_EMULATOR doesn't work ? Why
Eclipse / AVD has a Device ID ? And why Device ID is changing in this case
?
Thank you,
Paul.