Prerequisites

To follow this test, you'll need the following tools installed on your machine:

• Git (https://git-scm.com/)
• Node.js (https://nodejs.org/)

Getting started

1. You need to add the credentials in the test/test-cross-chain-call.test.js, which consist of the userKey and the projectKey. To get your user key, follow this tutorial. To get your project key, follow this tutorial.

It should look like this:

harbor = new Harbor({
  userKey: "cFeJWnDwQFVTSF2AabM2W5",
  projectKey: "fPMeKGPUfyBTCoq2omv3G4",
});

The above keys are for demonstration only. They don't actually work! Also, the Harbor SDK does not support parallel test execution, yet. But this is coming soon!

2. Set the testnet name value in the test/test-cross-chain-call.test.js file. You can do this by updating the TESTNET_NAME variable to a unique name of your choice. For example:

let TESTNET_NAME = ""

3. Install the project dependencies by running the following command:

yarn install

4. Finally, compile the contracts:

rm -rf artifacts && npx hardhat compile

Overview of contracts

You will be looking at two contracts, one on the Ethereum blockchain and another on the Polygon blockchain. The Ethereum contract will act as the message sender while the Polygon contract will act as the message receiver.

You can read the contracts in-depth if you'd like to learn more about them.

Testing

The test is located in the test/test-cross-chain-call.test.js. Open it and follow along!

Axelar Testnet configuration

Before you move on to running the tests, you need to know how you are applying the Axelar Testnet configuration that contains the 2 custom contracts.

The variable harborConfig contains the JSON:

const harborConfig = {
  bridges: [
    {
      name: "AXELAR",
      chains: ["ethereum", "polygon"],
    },
  ],
  chains: [
    {
      chain: "ethereum",
      config: {
        artifactsPath: "./artifacts/",
        deploy: {
          scripts: "./deploy/ethereum",
        },
        environment: {
          AXL_GATEWAY_ADDR: "$axl_gateway_addr",
          AXL_GAS_RECEIVER_ADDR: "$axl_gasReceiver_addr",
        },
      },
      tag: "v7",
    },
    {
      chain: "polygon",
      config: {
        artifactsPath: "./artifacts",
        deploy: {
          scripts: "./deploy/polygon",
        },
        environment: {
          AXL_GATEWAY_ADDR: "$axl_gateway_addr",
          AXL_GAS_RECEIVER_ADDR: "$axl_gasReceiver_addr",
        },
      },
      tag: "v7",
    },
  ],
};

This Testnet configuration contains two important attributes, bridges and chains:

• In bridges, you specify the name of bridge that you are applying along with the array of chains that you'd like to include in the bridge
• In chains, you configure each separate chain further with it's own artifacts and deployment scripts.
  • You must specify the AXL_GATEWAY_ADDR and AXL_GAS_RECEIVER_ADDR in the environment attribute.
    • This is because both contracts needs these arguments in it's constructor, otherwise they won't work with the Axelar protocol
  • Both their values $axl_gateway_addr and $axl_gasReceiver_addr are automatically filled by Harbor whilst it applies the Testnet

READ MORE ABOUT THE CONFIGURATION FILE HERE

Running the tests

To execute the test, tun the following command in your terminal:

yarn jest test/test-cross-chain-call.test.js

As explained above, this test applies the Axelar configuration with the custom contracts, checks for the chains / off-chain actors existence on the Testnet while also executing and asserting the cross-chain transaction from Ethereum to Polygon.

Overview of tests

Check if the Testnet is up with the right chains and off chain actors

After you apply the Testnet in the beforeAll function, you must check that the testnet, the chains and the off-chain actor (just the relayer) exist!

Check if the cross-chain message passing works

Next, you need to prove that the cross-chain message passing works. Your Ethereum contract, MessageSender, needs to send a message. After that transaction is made, the attribute value() is expected to change to the new message in the contract MessageReceiver on Polygon. Asserting that the MessageReceiver's value equals to the MESSAGE variable that was set in the test is enough to prove that the cross-chain transaction worked!