def _make_fasta(
    num_proteins, peptides, peptides_per_protein, random_state, prefix=""
):
    """Create a FASTA string from a set of peptides

    Parameters
    ----------
    num_proteins : int
        The number of proteins to generate.
    peptides : list of str
        A list of peptide sequences.
    peptides_per_protein: int
        The number of peptides per protein.
    random_state : numpy.random.Generator object
        The random state.
    prefix : str
        The prefix, if generating decoys

    Returns
    -------
    list of str
        A list of lines in a FASTA file.
    """
    lines = []
    for protein in range(num_proteins):
        lines.append(f">{prefix}sp|test|test_{protein}")
        lines.append(
            "".join(list(random_state.choice(peptides, peptides_per_protein)))
        )

    return lines