add test_util stubs for file open and append_line

src/test_utils.rs

@@ -8,6 +8,7 @@ use tempfile::{tempdir, TempDir};
 
 use crate::{
     errors::Error,
+    file::{FileAppendLineFn, FileOpenFn},
     network::{NetworkDownloadAsMp3Fn, NetworkFetchAsBytesFn, NetworkFetchAsTextFn},
     prelude::*,
 };
@@ -45,3 +46,9 @@ pub fn stub_fetch_as_bytes() -> NetworkFetchAsBytesFn {
 pub fn stub_download_as_mp3() -> NetworkDownloadAsMp3Fn {
     Box::new(|_url: &str| Err(Error::message("Not implemented")))
 }
+pub fn stub_file_open() -> FileOpenFn {
+    Box::new(|_path: &str| Err(Error::message("Not implemented")))
+}
+pub fn stub_file_append_line() -> FileAppendLineFn {
+    Box::new(|_: &str, _: &str| Err(Error::message("Not implemented")))
+}