The installation of a new cap for the Macondo went "extremely well" yesterday, BP told the New York Times. Now, the device will receive a series of integrity tests that could last from a few hours to two days.

What should you be watching for? BP wants to see high-pressure steadily build up under the cap. If they don't,  "BP engineers and government scientists will have compelling evidence that the well is damaged somewhere below the gulf floor, and oil and gas are leaking into the rock formation," writes the Washington Post's Joel Achenbach. That would mean that the flow of oil wouldn't be stanched until the completion of relief wells next month. 

"Everybody hope and pray that we see high pressures here," BP senior vice president Kent Wells  reportedly said in a Tuesday morning conference call.

Even under the best case scenario, the well blowout has already seriously damaged Gulf ecosystems. The low-end Department of Energy estimate is that more than 90 million gallons of oil have spilled into the gulf; other experts peg the flow much higher