def simple_vcf(tmp_path):
    """
    Pretends there is a variant at site 10 on the ref.

    This will overlap the read in simple_sam.
    """
    f = tmp_path / "simple.vcf"
    f.write_text('##fileformat=VCFv4.2\n' +
        '##FILTER=<ID=PASS,Description="All filters passed">\n' +
        '##contig=<ID=ref,length=45>\n' +
        '##FORMAT=<ID=GT,Number=1,Type=String,Description="Genotype">\n' +
        '##FORMAT=<ID=AD,Number=R,Type=Integer,Description="Allelic depths for the ref and alt alleles in the order listed">\n' +
        "#CHROM\tPOS\tID\tREF\tALT\tQUAL\tFILTER\tINFO\tFORMAT\tsyndip\n" +
        "ref\t10\t.\tG\tT\t30\t.\t.\tGT:AD\t0|1:1,1\n")
    return str(f)