added mock_network_download_as_mp3

src/test_utils.rs

@@ -69,6 +69,10 @@ pub fn mock_file_open(real_paths: Vec<String>) -> FileOpenFn {
     })
 }
 
+pub fn mock_network_download_as_mp3() -> NetworkDownloadAsMp3Fn {
+    Box::new(|_url| Ok(()))
+}
+
 pub fn stub_network_fetch_as_bytes() -> NetworkFetchAsBytesFn {
     Box::new(|url: &str| {
         Err(Error::message(