diff --git a/scubainit-rs/src/groups.rs b/scubainit-rs/src/groups.rs
index 3aefe38c..3a997ac6 100644
--- a/scubainit-rs/src/groups.rs
+++ b/scubainit-rs/src/groups.rs
@@ -1,8 +1,7 @@
 use std::fs::File;
 use std::io::{BufRead, BufReader, Write};
-use std::path::Path;
 
-#[derive(Debug)]
+#[derive(Debug, Eq, PartialEq)]
 pub struct GroupEntry {
     pub name: String,
     pub passwd: String,
@@ -10,16 +9,15 @@ pub struct GroupEntry {
     pub members: Vec<String>,
 }
 
-pub struct GroupFileReader {
-    reader: BufReader<File>,
+pub struct GroupFileReader<'a> {
+    reader: BufReader<&'a File>,
 }
 
-impl GroupFileReader {
-    pub fn open<P: AsRef<Path>>(path: P) -> std::io::Result<GroupFileReader> {
-        let f = File::open(path)?;
-        Ok(GroupFileReader {
-            reader: BufReader::new(f),
-        })
+impl GroupFileReader<'_> {
+    pub fn new(file: &File) -> GroupFileReader {
+        GroupFileReader {
+            reader: BufReader::new(file),
+        }
     }
 }
 
@@ -58,7 +56,7 @@ impl GroupEntry {
     }
 }
 
-impl Iterator for GroupFileReader {
+impl Iterator for GroupFileReader<'_> {
     type Item = GroupEntry;
 
     fn next(&mut self) -> Option<Self::Item> {
diff --git a/scubainit-rs/src/main.rs b/scubainit-rs/src/main.rs
index b91ca373..c01851a8 100644
--- a/scubainit-rs/src/main.rs
+++ b/scubainit-rs/src/main.rs
@@ -56,6 +56,14 @@ fn main() -> Result<()> {
     Ok(())
 }
 
+
+/// Opens a file for reading and appeneding.
+///
+/// The file is created if it does not exist.
+fn open_read_append<P: AsRef<Path>>(path: P) -> std::io::Result<fs::File> {
+    fs::File::options().append(true).read(true).create(true).open(path)
+}
+
 struct UserInfo {
     uid: u32,
     gid: u32,
@@ -82,10 +90,10 @@ impl UserInfo {
         let group_name = &self.group;
         let gid = self.gid;
 
+        let file = open_read_append(ETC_GROUP)?;
+
         // Try to find a conflicting group (one matching name or gid).
-        // TODO: Skip if file is missing
-        // TODO: Can we open the file once (like fopen(path, "a+"))
-        let mut reader = groups::GroupFileReader::open(ETC_GROUP)?;
+        let mut reader = groups::GroupFileReader::new(&file);
         for grp in reader {
             let name_matches = grp.name.as_str() == group_name;
             let gid_matches = grp.gid == gid;
@@ -110,7 +118,6 @@ impl UserInfo {
             gid: gid,
             members: Vec::new(),
         };
-        let file = fs::File::options().append(true).create(true).open(ETC_GROUP)?;
         let mut writer = groups::GroupFileWriter::new(&file);
         Ok(writer.write(&grp)?)
     }
diff --git a/scubainit-rs/tests/groups.rs b/scubainit-rs/tests/groups.rs
index 2e5c1832..6b5c8032 100644
--- a/scubainit-rs/tests/groups.rs
+++ b/scubainit-rs/tests/groups.rs
@@ -1,5 +1,8 @@
 use anyhow::Result;
-use std::io::{Read, Seek};
+use std::fs;
+use std::io::{BufRead, BufReader};
+use std::io::{Read, Seek, Write};
+use std::path::Path;
 use tempfile;
 
 use scubainit_rs::groups::{GroupEntry, GroupFileReader, GroupFileWriter};
@@ -16,14 +19,16 @@ macro_rules! vec_of_strings {
 
 #[test]
 fn test_group_empty() -> Result<()> {
-    let mut reader = GroupFileReader::open("testdata/group_empty")?;
+    let file = fs::File::open("testdata/group_empty")?;
+    let mut reader = GroupFileReader::new(&file);
     assert!(reader.next().is_none());
     Ok(())
 }
 
 #[test]
 fn test_group1() -> Result<()> {
-    let mut reader = GroupFileReader::open("testdata/group1")?;
+    let file = fs::File::open("testdata/group1")?;
+    let mut reader = GroupFileReader::new(&file);
 
     let g = reader.next().unwrap();
     assert_eq!(g.name, "foo");
@@ -67,5 +72,87 @@ fn test_write() -> Result<()> {
     assert_eq!(buffer, "foo:x:1234:moe,larry,shemp\n");
 
 
+    Ok(())
+}
+
+#[test]
+fn test_write_read() -> Result<()> {
+    let mut file = tempfile::tempfile()?;
+
+    let mut writer = GroupFileWriter::new(&file);
+    let grp_w = GroupEntry {
+        name: "foo".to_string(),
+        passwd: "x".to_string(),
+        gid: 1234,
+        members: vec_of_strings!["moe", "larry", "shemp"],
+    };
+    writer.write(&grp_w)?;
+
+    file.rewind()?;
+
+    let mut reader = GroupFileReader::new(&file);
+    let grp_r = reader.next().unwrap();
+
+    assert_eq!(grp_w, grp_r);
+    Ok(())
+}
+
+// TODO: DRY
+fn open_read_append<P: AsRef<Path>>(path: P) -> std::io::Result<fs::File> {
+    fs::File::options().append(true).read(true).create(true).open(path)
+}
+
+#[test]
+fn test_read_write() -> Result<()> {
+    const LINE1: &str = "foo:x:1234:moe,larry,shemp";
+    const LINE2: &str = "bar:x:2345:moe";
+
+    // First populate a file with some content
+    let mut content = tempfile::NamedTempFile::new()?;
+    writeln!(content, "{LINE1}").unwrap();
+    writeln!(content, "{LINE2}").unwrap();
+
+    // Process the tempfile
+    {
+        let file = open_read_append(content.path())?;
+
+        // Now read
+        let mut reader = GroupFileReader::new(&file);
+
+        let r = reader.next().unwrap();
+        assert_eq!(r.name, "foo");
+
+        let r = reader.next().unwrap();
+        assert_eq!(r.name, "bar");
+
+        // Now write
+        let mut writer = GroupFileWriter::new(&file);
+        let new_grp = GroupEntry {
+            name: "snap".to_string(),
+            passwd: "x".to_string(),
+            gid: 3456,
+            members: vec_of_strings!["crackle", "pop"],
+        };
+        writer.write(&new_grp)?;
+    }
+
+    content.rewind()?;
+
+    // Read back the modified file and verify
+    let mut content_reader = BufReader::new(content);
+    let mut line = String::with_capacity(128);
+
+    line.clear();
+    content_reader.read_line(&mut line)?;
+    assert_eq!(line.trim_end(), LINE1);
+
+    line.clear();
+    content_reader.read_line(&mut line)?;
+    assert_eq!(line.trim_end(), LINE2);
+
+    line.clear();
+    content_reader.read_line(&mut line)?;
+    assert_eq!(line.trim_end(), "snap:x:3456:crackle,pop");
+
     Ok(())
 }