How to test a function that is expected to return error?

Question

I got two questions :

First :

I have some custom error type declared in the smart contract and I want to check the appropriate error to be returned from the function call , I wonder how can I get the response ?

For example :

#[msg("Username length should not exceed 100 characters")]
PhoneNumberLengthExceeded,

And I have this test :

        await program.methods.signUp("sajjad", "09146979106555555555", "").accounts({

        user: secondUser.publicKey,
        authority: provider.wallet.publicKey,
        systemProgram: SystemProgram.programId,
        clock: anchor.web3.SYSVAR_CLOCK_PUBKEY,

    }).signers([secondUser]).rpc({ skipPreflight: true });

which throws PhoneNumberLengthExceeded and messes up the test .

Second how can I write tests for the build in errors ?

which is thrown for example when the second user is being created with the first user Keypair which is obvious .

Answer 1

There are a few ways to assert errors. Here is one from Anchor's tic-tac-toe example:

try {
    await program.methods.signUp("sajjad", "09146979106555555555", "").accounts({
        user: secondUser.publicKey,
        authority: provider.wallet.publicKey,
        systemProgram: SystemProgram.programId,
        clock: anchor.web3.SYSVAR_CLOCK_PUBKEY,
    }).signers([secondUser]).rpc({ skipPreflight: true });
    
    // we use this to make sure we definitely throw an error
    chai.assert(false, "should've failed but didn't ")
} catch (err) {
    expect(err).to.be.instanceOf(AnchorError)
    expect((err as AnchorError).error.errorCode.number).to.equal(6000)
}

The errorCode.number is the ordinal value of your specific Errors enum or you can be explicit about it like this:

#[msg("Username length should not exceed 100 characters")]
PhoneNumberLengthExceeded = 6000,

You can also do an assertion on errorCode.message to match the one defined in the macro if you find that more developer-friendly.

Answer 2

try {
  await program.methods
    .signUp("sajjad", "09146979106555555555", "")
    .accounts({
        user: secondUser.publicKey,
        authority: provider.wallet.publicKey,
        systemProgram: SystemProgram.programId,
        clock: anchor.web3.SYSVAR_CLOCK_PUBKEY,

    }).signers([secondUser]).rpc({ skipPreflight: true });

} catch (_err) {
   // do anything with error message here
   console.log(_err);
}