Pipe expansion, Pressure decreases with temperature increase
Fluid expansion, pressure increases with temperature increase, for most fluids, but some (yes water is one) depend on the temperature and the temperature range during the test. The resulting pressure varies with temperature depending on the temperature expansion coefficients of one in relation to the other.
For a 10 minute test, I doubt that temperature will stabilize enough to get much of a test, or really be a factor worth considering, as there shouldn't be much temperature change in 10 minutes, other than to determine if there is tightness or not. That would hardly be enough time for the pipe temperature and fluid temperature to equalize.
Therefore, if its just a short time tightness test, I wouldn't worry much about temperature at all. If you get any effect, what you're measuring would not give an accurate indication of leaks anyway.
"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/