How do I write tests correctly? Getting ChainMismatchError using test client.

[9inpachi]

Hi all,

I am new to web3 and struggling a bit to find the right way to write tests for contract transactions that are done through viem.

I want to test the following code.

class Client {
  constructor(private walletClient: WalletClient) {}

  public deposit(walletAddress: Address) {
    const contract = getContract({
      address: '0x...',
      abi: ...,
      client: {
        // Test client passed through the constructor.
        wallet: this.walletClient,
      },
    });
    
    const transact = async (value: bigint) =>
      await contract.write.deposit([walletAddress], {
        account: walletAddress,
        chain: this.walletClient.chain,
        value,
      });
    
    const estimate = async () =>
      await contract.estimateGas.deposit([walletAddress], {
        account: walletAddress,
      });
    
    return { transact, estimate };
  }
}

This is the test I am trying to write.

export const setupTestClient = (requestMock: EIP1193RequestFn = jest.fn()) => {
  return createTestClient({
    mode: 'anvil',
    chain: anvil,
    transport: custom({ request: requestMock }),
  });
};

export const setupTestWalletClient = (
  requestMock: EIP1193RequestFn = jest.fn(),
) => {
  const client = setupTestClient(requestMock);
  return client.extend(walletActions) as WalletClient;
};

it('should deposit', async () => {
  const mockAddress = '0xEB77D02f8122B32273444a1b544C147Fb559CB41';
  const mockGas = BigInt(1);

  // `transact` aka `deposit` function of the contract returns an address.
  const walletRequest = jest.fn().mockReturnValue(mockAddress);
  const walletClient = setupTestWalletClient(walletRequest);

  const client = new Client(walletClient);

  const { transact, estimate } = client.deposit(mockAddress);

  expect(await transact(BigInt(1))).toBe(mockAddress);
  expect(await estimate()).toBe(mockGas);
});

However, I get the following error.

ChainMismatchError: The current chain of the wallet (id: 1.344284755342623e+48) does not match the target chain for the transaction (id: 31337 – Anvil).

Any idea what I might be doing wrong? I have been trying to look around what's the best way to write tests for viem-based code like this but haven't been able to find any useful examples to use as reference.