Reading msg! logs in anchor test: confirmTransaction then getTransaction with maxSupportedTransactionVersion 0 for meta.logMessages

Symptom: in an Anchor mocha test you want to assert that an instruction emitted a specific msg! line, but there is no log on the object returned by .rpc() (it is only a signature string), and a naive connection.getTransaction(sig) returns null or throws about an unsupported transaction version.

Cause: .rpc() resolves as soon as the transaction is sent/processed, before the RPC node will serve it at the commitment you query, and getTransaction refuses to return versioned (v0) transactions unless you opt in explicitly.

Working pattern:

const sig = await program.methods.setFavorites(new anchor.BN(23), 'red').rpc();
const connection = program.provider.connection;
const bh = await connection.getLatestBlockhash();
await connection.confirmTransaction({ signature: sig, blockhash: bh.blockhash, lastValidBlockHeight: bh.lastValidBlockHeight }, 'confirmed');
const tx = await connection.getTransaction(sig, { commitment: 'confirmed', maxSupportedTransactionVersion: 0 });
const logs = tx?.meta?.logMessages ?? [];

Two details that cost time: the commitment passed to getTransaction must be at least as weak as the level you confirmed at (processed is not allowed there), and every program log is prefixed by the runtime, so entries look like Program log: The number is: 23, the color is: red. An assertion on the bare string fails; match with logs.some(l => l.includes('The number is: 23')).

Applies to @solana/web3.js 1.x with Anchor 0.29-0.32. Under the newer @solana/kit RPC API the same idea holds but the method is getTransaction on the RPC object with the same maxSupportedTransactionVersion argument.

Source: adapted from a Stack Exchange answer by amilz (question by mikemaccana), https://solana.stackexchange.com/questions/10222/how-can-i-check-the-transaction-logs-in-anchor-test — CC BY-SA 4.0