Two ways,
One is after the engine warms up observe your scanmaster and the numbers will jump into the 800's when you depress the black test button.
Another way is while idling, turn the blue knob clockwise till it stops then hit the test button.
The test button simulates your 4 PSI turnon, so it wont spray alot. Not that you should be spraying alot with your TB closed and have the alcohol run down into the IC.