diff --git a/build.rs b/build.rs
deleted file mode 100644
index 8f19e94..0000000
--- a/build.rs
+++ /dev/null
@@ -1,6 +0,0 @@
-use pyo3_build_config;
-
-fn main() {
-    // If you have an existing build.rs file, just add this line to it.
-    pyo3_build_config::use_pyo3_cfgs();
-}
diff --git a/src/directsketch.rs b/src/directsketch.rs
index 788974d..202762a 100644
--- a/src/directsketch.rs
+++ b/src/directsketch.rs
@@ -1,10 +1,8 @@
 use anyhow::{anyhow, bail, Context, Error, Result};
-use async_zip::base::write::{self, ZipFileWriter};
-use async_zip::Compression;
-use async_zip::{ZipDateTime, ZipEntryBuilder};
+use async_zip::base::write::ZipFileWriter;
+use async_zip::{Compression, ZipDateTime, ZipEntryBuilder};
 use camino::Utf8PathBuf as PathBuf;
 use chrono::Utc;
-use md5;
 use needletail::parse_fastx_reader;
 use regex::Regex;
 use reqwest::Client;
@@ -12,23 +10,21 @@ use std::collections::HashMap;
 use std::fs::{self, create_dir_all};
 use std::io::Cursor;
 use std::path::Path;
+use std::sync::Arc;
 use tokio::fs::File;
-use tokio::task;
+use tokio::io::{AsyncWriteExt, BufWriter};
+use tokio::sync::Semaphore;
+use tokio::time::Duration;
 use tokio_util::compat::Compat;
 
 use pyo3::prelude::*;
 
-use std::sync::Arc;
-use tokio::io::{AsyncWriteExt, BufWriter};
-
-use tokio::sync::Semaphore;
-use tokio::time::{interval, Duration};
-
 use sourmash::manifest::{Manifest, Record};
 use sourmash::signature::Signature;
 
 use crate::utils::{build_siginfo, load_accession_info, parse_params_str};
 
+#[allow(dead_code)]
 enum GenBankFileType {
     Genomic,
     Protein,
@@ -449,7 +445,7 @@ async fn write_sig(
 pub fn sigwriter_handle(
     mut recv_sigs: tokio::sync::mpsc::Receiver<Vec<Signature>>,
     output_sigs: String,
-    mut error_sender: tokio::sync::mpsc::Sender<anyhow::Error>,
+    error_sender: tokio::sync::mpsc::Sender<anyhow::Error>,
 ) -> tokio::task::JoinHandle<()> {
     tokio::spawn(async move {
         let mut md5sum_occurrences = HashMap::new();
@@ -481,7 +477,7 @@ pub fn sigwriter_handle(
                     Ok(_) => wrote_sigs = true,
                     Err(e) => {
                         let error = e.context("Error processing signature");
-                        if let Err(send_error) = error_sender.send(error).await {
+                        if (error_sender.send(error).await).is_err() {
                             return; // Exit on failure to send error
                         }
                     }
@@ -530,7 +526,7 @@ pub fn sigwriter_handle(
 pub fn failures_handle(
     failed_csv: String,
     mut recv_failed: tokio::sync::mpsc::Receiver<FailedDownload>,
-    mut error_sender: tokio::sync::mpsc::Sender<Error>, // Additional parameter for error channel
+    error_sender: tokio::sync::mpsc::Sender<Error>, // Additional parameter for error channel
 ) -> tokio::task::JoinHandle<()> {
     tokio::spawn(async move {
         match File::create(&failed_csv).await {
@@ -698,7 +694,7 @@ pub async fn download_and_sketch(
                     }
                 }
                 Err(e) => {
-                    let _ = send_errors.send(e.into()).await;
+                    let _ = send_errors.send(e).await;
                 }
             }
             drop(send_errors);
diff --git a/src/lib.rs b/src/lib.rs
index 9cb329d..6977c4e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -18,18 +18,32 @@ lazy_static! {
 #[pyfunction]
 fn set_tokio_thread_pool(num_threads: usize) -> PyResult<usize> {
     let mut rt_lock = GLOBAL_RUNTIME.lock().unwrap();
-    if rt_lock.is_none() {
-        // Only initialize the runtime if it has not been initialized already
-        let runtime = Builder::new_multi_thread()
-            .worker_threads(num_threads)
-            .enable_all()
-            .build()
-            .map_err(|e| PyErr::new::<PyRuntimeError, _>(e))?;
 
-        *rt_lock = Some(runtime);
+    // Check if pytest is running
+    let pytest_running = std::env::var("PYTEST_RUNNING").is_ok();
+
+    // Check if runtime is already initialized
+    if rt_lock.is_some() {
+        if pytest_running {
+            // If pytest is running, simply return the number of threads without error
+            return Ok(num_threads);
+        } else {
+            // If not under pytest, return an error on reinitialization attempts
+            return Err(PyErr::new::<PyRuntimeError, _>(
+                "Tokio runtime is already initialized.",
+            ));
+        }
     }
 
-    // Return the number of threads, which is now guaranteed to be set
+    // Initialize the runtime if not already initialized
+    let runtime = Builder::new_multi_thread()
+        .worker_threads(num_threads)
+        .enable_all()
+        .build()
+        .map_err(PyErr::new::<PyRuntimeError, _>)?;
+
+    *rt_lock = Some(runtime);
+
     Ok(num_threads)
 }
 
diff --git a/tests/conftest.py b/tests/conftest.py
index 49cb49f..3f90580 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -14,3 +14,6 @@ def runtmp():
 # Set environment variable PYTEST_RUNNING
 def pytest_configure(config):
     os.environ["PYTEST_RUNNING"] = "1"
+
+def pytest_unconfigure(config):
+    del os.environ["PYTEST_RUNNING"]