def benchmark_rank_by_mean(benchmark_snapshot_df):
    """Returns ranking of fuzzers based on mean coverage."""
    assert benchmark_snapshot_df.time.nunique() == 1, 'Not a snapshot!'
    means = benchmark_snapshot_df.groupby('fuzzer')['edges_covered'].mean()
    means.rename('mean cov', inplace=True)
    return means.sort_values(ascending=False)