tmpfiles: Add a unit test

This is way faster to test than a full compose build.

rust/src/tmpfiles.rs

@@ -106,6 +106,8 @@ fn tmpfiles_entry_get_path(line: &str) -> Result<&str> {
 
 #[cfg(test)]
 mod tests {
+    use rustix::fd::AsRawFd;
+
     use super::*;
     #[test]
     fn test_tmpfiles_entry_get_path() {
@@ -119,4 +121,55 @@ mod tests {
             assert_eq!(path, expected, "Input: {input}");
         }
     }
+
+    fn newroot() -> Result<cap_std_ext::cap_tempfile::TempDir> {
+        let root = cap_std_ext::cap_tempfile::tempdir(cap_std::ambient_authority())?;
+        root.create_dir_all(RPMOSTREE_TMPFILESD)?;
+        root.create_dir_all(TMPFILESD)?;
+        Ok(root)
+    }
+
+    #[test]
+    fn test_deduplicate_noop() -> Result<()> {
+        let root = &newroot()?;
+        deduplicate_tmpfiles_entries(root.as_raw_fd())?;
+        Ok(())
+    }
+
+    // The first and 3rd are duplicates
+    const PKG_FILESYSTEM_CONTENTS: &str = indoc::indoc! { r#"
+d /var/cache 0755 root root - -
+d /var/lib/games 0755 root root - -
+d /var/tmp 1777 root root - -
+d /var/spool/mail 0775 root mail - -
+"# };
+    const VAR_CONF: &str = indoc::indoc! { r#"
+d /var/cache 0755 - - -
+"# };
+    const TMP_CONF: &str = indoc::indoc! { r#"
+q /var/tmp 1777 root root 30d
+"# };
+
+    #[test]
+    fn test_deduplicate() -> Result<()> {
+        let root = &newroot()?;
+        let rpmostree_tmpfiles_dir = root.open_dir(RPMOSTREE_TMPFILESD)?;
+        let tmpfiles_dir = root.open_dir(TMPFILESD)?;
+        rpmostree_tmpfiles_dir
+            .atomic_write(format!("pkg-filesystem.conf"), PKG_FILESYSTEM_CONTENTS)?;
+        tmpfiles_dir.atomic_write("var.conf", VAR_CONF)?;
+        tmpfiles_dir.atomic_write("tmp.conf", TMP_CONF)?;
+        assert!(!tmpfiles_dir.try_exists(AUTOVAR_PATH)?);
+        deduplicate_tmpfiles_entries(root.as_raw_fd())?;
+        let contents = tmpfiles_dir.read_to_string(AUTOVAR_PATH).unwrap();
+        assert!(contents.contains("# This file was generated by rpm-ostree."));
+        let entries = contents
+            .lines()
+            .filter(|l| !(l.is_empty() || l.starts_with('#')))
+            .collect::<Vec<_>>();
+        assert_eq!(entries.len(), 2);
+        assert_eq!(entries[0], "d /var/lib/games 0755 root root - -");
+        assert_eq!(entries[1], "d /var/spool/mail 0775 root mail - -");
+        Ok(())
+    }
 }