diff --git a/src/group/mod.rs b/src/group/mod.rs
index 7aaae21..90e6725 100644
--- a/src/group/mod.rs
+++ b/src/group/mod.rs
@@ -102,11 +102,11 @@ impl NewFromString for Group {
         println!("{}", &line);
         let elements: Vec<String> = line.split(':').map(ToString::to_string).collect();
         if elements.len() == 4 {
-            Ok(Group {
+            Ok(Self {
                 groupname: Groupname::try_from(elements.get(0).unwrap().to_string())?,
                 password: crate::Password::Disabled,
                 gid: crate::Gid::try_from(elements.get(2).unwrap().to_string())?,
-                members: parse_members_list(elements.get(3).unwrap().to_string()),
+                members: parse_members_list(elements.get(3).unwrap()),
             })
         } else {
             Err(UserLibError::Message(format!(
@@ -118,13 +118,15 @@ impl NewFromString for Group {
     }
 }
 
-fn parse_members_list(source: String) -> Vec<crate::Username> {
+fn parse_members_list(source: &str) -> Vec<crate::Username> {
     let mut res = vec![];
-    for mem in source
-        .split(',')
-        .filter(|x| !x.is_empty())
-        .map(ToString::to_string)
-    {
+    for mem in source.split(',').filter_map(|x| {
+        if x.is_empty() {
+            None
+        } else {
+            Some(x.to_string())
+        }
+    }) {
         res.push(crate::Username::try_from(mem).expect("failed to parse username"));
     }
     res
diff --git a/src/user/passwd_fields.rs b/src/user/passwd_fields.rs
index 811b8cf..3e67e8c 100644
--- a/src/user/passwd_fields.rs
+++ b/src/user/passwd_fields.rs
@@ -63,9 +63,9 @@ pub enum Password {
 impl Display for Password {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
-            Password::Encrypted(EncryptedPassword { password }) => write!(f, "{}", password,),
-            Password::Shadow(_) => write!(f, "x"),
-            Password::Disabled => write!(f, "x"),
+            Self::Encrypted(EncryptedPassword { password }) => write!(f, "{}", password,),
+            Self::Shadow(_) => write!(f, "x"),
+            Self::Disabled => write!(f, "x"),
         }
     }
 }
@@ -183,7 +183,7 @@ impl Display for ShellPath {
 impl TryFrom<String> for ShellPath {
     type Error = UserLibError;
     fn try_from(source: String) -> std::result::Result<Self, Self::Error> {
-        Ok(ShellPath { shell: source })
+        Ok(Self { shell: source })
     }
 }
 
diff --git a/src/user/shadow_fields.rs b/src/user/shadow_fields.rs
index 3e0494f..423af98 100644
--- a/src/user/shadow_fields.rs
+++ b/src/user/shadow_fields.rs
@@ -97,7 +97,7 @@ impl NewFromString for Shadow {
         let elements: Vec<String> = line.split(':').map(ToString::to_string).collect();
         if elements.len() == 9 {
             let extra = elements.get(8).unwrap();
-            Ok(Shadow {
+            Ok(Self {
                 username: crate::Username::try_from(elements.get(0).unwrap().to_string())?,
                 password: crate::EncryptedPassword::try_from(elements.get(1).unwrap().to_string())?,
                 last_change: date_since_epoch(elements.get(2).unwrap()),
diff --git a/src/userlib.rs b/src/userlib.rs
index 93be679..82c3d24 100644
--- a/src/userlib.rs
+++ b/src/userlib.rs
@@ -38,11 +38,11 @@ impl Default for Files {
 impl UserDBLocal {
     #[must_use]
     pub fn import_from_strings(
-        passwd_content: String,
-        shadow_content: String,
-        group_content: String,
+        passwd_content: &str,
+        shadow_content: &str,
+        group_content: &str,
     ) -> Self {
-        let res = UserDBLocal {
+        let res = Self {
             source_files: Files {
                 passwd: None,
                 group: None,
@@ -128,6 +128,10 @@ impl UserDBLocal {
     }
 }
 
+/// Try to parse a String into some Object
+///
+/// # Errors
+/// if the parsing failed a [`UserLibError::Message`] is returned containing a more detailed error message.
 pub trait NewFromString {
     fn new_from_string(line: String) -> Result<Self, crate::UserLibError>
     where
@@ -153,7 +157,7 @@ where
 
 #[test]
 fn test_creator_user_db_local() {
-    let data = UserDBLocal::import_from_strings("testuser:x:1001:1001:full Name,004,000342,001-2312,myemail@test.com:/home/test:/bin/test".to_string(), "test:!!$6$/RotIe4VZzzAun4W$7YUONvru1rDnllN5TvrnOMsWUD5wSDUPAD6t6/Xwsr/0QOuWF3HcfAhypRkGa8G1B9qqWV5kZSnCb8GKMN9N61:18260:0:99999:7:::".to_string(), "teste:x:1002:test,teste".to_string());
+    let data = UserDBLocal::import_from_strings("testuser:x:1001:1001:full Name,004,000342,001-2312,myemail@test.com:/home/test:/bin/test", "test:!!$6$/RotIe4VZzzAun4W$7YUONvru1rDnllN5TvrnOMsWUD5wSDUPAD6t6/Xwsr/0QOuWF3HcfAhypRkGa8G1B9qqWV5kZSnCb8GKMN9N61:18260:0:99999:7:::", "teste:x:1002:test,teste");
     assert_eq!(
         data.passwd_entries.get(0).unwrap().get_username(),
         "testuser"
@@ -172,6 +176,6 @@ fn test_parsing_local_database() {
     let mut group_reader = BufReader::new(group_file);
     let mut my_group_lines = "".to_string();
     group_reader.read_to_string(&mut my_group_lines).unwrap();
-    let data = UserDBLocal::import_from_strings(my_passwd_lines, "".to_string(), my_group_lines);
+    let data = UserDBLocal::import_from_strings(&my_passwd_lines, "", &my_group_lines);
     assert_eq!(data.group_entries.get(0).unwrap().get_groupname(), "root");
 }