Testing LayerZero contracts using a mock endpoint

In this tutorial, we will:

1. Implement a simple example of cross-chain communication using two smart contracts.
2. Test out the contracts using LZEndpointMock.sol.

What are we building?

We will implement two smart contracts, OmniCounter_Mumbai and OmniCounter_Sepolia, to be deployed on Mumbai and Sepolia respectively.

Both of them have a state variable named counter declared, which is initialized to 0 by default. We want to leverage the LayerZero protocol so that when the incrementCounter function is called on either of the two contracts, the counter variable on the other contract is incremented by 1.

This will require a cross-chain message to be sent using LayerZero, and we will check if our contracts are correctly configured to receive and process these messages using the LZEndpointMock.sol contract.