Party in government pursues opposition's policies

When parties hust for election, they often criticise the party in power and give dire prognostications of the consequences of current policy. However, if they then win the election, no-one gets to find out if they were right. They also tend to make certain statements while in opposition concerning what the current government are doing wrong, then fail to follow up what they said once they get voted in. Now suppose the term of a government was divided in half. In the first half, they must follow the policies of the former government as they understand them and have portrayed them, thereby providing evidence for or against their claims. In the other half, they get to undo everything they did in the first half by pursuing their own policies as stated while in opposition - not a published manifesto, what they actually said, for whatever reason. We still get full terms of government pursuing the policies we voted for (insofar as we do anyway), just deferred by half a term, so it remains as democratic as it ever was. In the meantime, the public gets to judge if the party was right. Moreover, if the previous government's policies proved to have popular results, the current government then loses out when it reverses everything, which it's committed itself to do a couple of years previously. It also stops the government from simply saying one thing in opposition and doing something else once elected - well, strictly speaking, a couple of years later. Therefore, what the politicians say when they're in opposition can be trusted as it constitutes their actual manifesto.