The pullout from deep sea mining exploration by Petrobras was this week's test for Shearer - and mining, with its inherent conflict of jobs versus environment, is one area in which the tension between the two parties is most obvious.
Shearer also has to counter the scare campaign National is already running on the potential dangers of that coalition - and on that front, Shearer has at least put one peg in the ground, with a solid "no" when asked about Green co-leader Russel Norman's desire for the finance job in a future Government.
In between painting apocalyptic scenarios of that coalition, Key was engaged in a game of Cluedo - the spies version.
Sightings of a United States Government jet at Wellington Airport prompted inevitable questions about the passengers and why they were here.
Key took his role as game master very seriously. He gave out little dribbles of hints, one by one. He let slip it was something to do with intelligence agencies. Then he said it was no secret at all: the plane's very existence indicated there was no secrecy, because what fool would leave a distinctive jet sitting on the tarmac if they wanted to be sneaky?
Key's answers made up for what the plane lacked in secrecy. He claimed he did not know who was at the meeting, how they got there, or what the meetings were about. He had not seen Colonel Mustard, he did not know whether the library had been breached, he could not say whether it was tomato sauce or blood on the candlestick.
Just as in Cluedo, the answers were on a piece of paper somewhere but he couldn't really be bothered looking at it.
Intrigued by private jets arriving in the dead of night and pieces of paper the Prime Minister would not look at, the air of mystery built.
"Go to the United States Embassy," Key suggested, guru-like, to those seeking further enlightenment.
Those who did go to the US Embassy discovered nothing more than what their eyes had already told them: a US Government jet had been on the tarmac at Wellington Airport.
By now the game was more important than the answer. The more he refused to answer, the more he was asked. He knew full well that had he said who the visitor was from the beginning - or simply refused point-blank to answer at the start - it was highly likely the media would have yawned and hunted for another mystery.
However, the bonus in it for the Prime Minister was that it was a wonderful decoy. Every question about the jet, and the people it had disgorged onto an unwitting Wellington, was a question that wasn't about jobs, whether the surplus goal was now as wobbly as a trifle, whether New Zealand was 100 per cent pure, or that perennial - how his plans to stem the brain drain to Australia were shaping up.
He had nothing to lose by dodging such questions, beyond adding to the general impression that when it came to the whims of America, he was as pliable as a Len Lye wind wand.
Finally, after three days, the end of the game was in sight. Key had looked at the piece of paper and discovered there was a range of officials here, from a range of countries, for a range of "routine meetings".
Routine maybe, but it was "standard practice" to be secret squirrel about it all.