Question about toThrow assertion "problem"

[asciito]

This is a fragment of a package that I'm working on, the "problem" that I have is that this code is failing, and this is the message:

Failed asserting that 'This is a custom exception' [ASCII](length: 26) contains "Asciito\SimpleGenerators\Clients\Contracts\Exceptions\ClientException" [ASCII](length: 69).

So, I want to know if toThrow also works with interfaces, but for want I read in the source code, this should be possible.

    $client = TextGenerator::fakeClient([
        ClientFakeException::make('fake', 'This is a custom exception'),
    ]);

    $generator = TextGenerator::make('throwable', $client);

    expect(fn() => $generator->prompt('This is just a fake prompt'))
        ->toThrow(
            ClientException::class,
            'This is a custom exception',
        );

is there something that I'm missing?