fix: get_many

Author: wendajiang

src/cmd/test.rs

@@ -43,11 +43,12 @@ pub fn make_subcommand() -> Command {
 
 // test command implementation
 pub fn execute(args: &ArgMatches) -> Result<()> {
-    let library_paths: Vec<&str> = args
-        .get_many::<String>("library-path")
-        .unwrap()
-        .map(|s| s.as_str())
-        .collect();
+    let library_paths: Vec<&str> = if let Some(it) = args.get_many::<String>("library-path") {
+        it.map(|s| s.as_str()).collect()
+    } else {
+        vec![]
+    };
+
     let chapter: Option<&str> = args.get_one::<String>("chapter").map(|s| s.as_str());
 
     let book_dir = get_book_dir(args);