In truffle console you can do the following.
1.Get a deployed instance of the contract and store it in a variable (coin).
MetaCoin.deployed().then(function(instance) {coin=instance;}); 2.Now execute the addEntity function with your own variables.
coin.addEntity('x', 'y', 'z'); When this is executed it will show you a transaction receipt (or errors if any occurred).
3.Check the entities mapping for the new entity.
coin.entities(1);
This shows you the entity that you just created based on the increment value of entitiesCount variable.
If you want to test with specific gas and account settings you can modify the call to addEntity function to include account and gas values.
coin.addEntity('x','y','z', {from:web3.eth.accounts[0], gas:500000, gasPrice: web3.toWei(1,"Gwei")})