ProgramTest does not run program -- idles until RPC Deadline is Exceeded

Hello. I am implementing tests for a Solana program and whenever i run a transaction (be it either with BanksClient::process_transaction or with BanksClient::process_transaction_with_commitment_and_context) I end up with the test idling until the RPC client returns because the Deadline has exceeded.
Currently I shortened my entrypoint to:

entrypoint!(process_instruction)

pub fn process_instruction(
    program_id: &Pubkey,
    accounts: &[AccountInfo],
    instruction_data: &[u8],
) -> ProgramResult {
    solana_program::msg!("Running entrypoint");
    Ok(())
}

I’ve checked with strings and objdump and both the entrypoint and the message are in the binary, but I can’t get it to run with cargo test or cargo tests.
The test is set up like this:

let program_id = Pubkey::new_unique();
let mut test = ProgramTest::new(
  "program_name",
  program_id,
  processor!(process_instruction)
);

the problem occurs when

banks_client.process_transaction(transaction).await.unwrap()

is called. Thank you in advance for your help