Add test for ensuring consistent G/UID mappings

Cargo.toml

@@ -59,6 +59,11 @@ name = "net_without_namespaces"
 path = "tests/net_without_namespaces.rs"
 harness = false
 
+[[test]]
+name = "consistent_id_mappings"
+path = "tests/consistent_id_mappings.rs"
+harness = false
+
 [target.'cfg(target_os = "linux")'.dependencies]
 seccompiler = "0.2.0"
 landlock = "0.2.0"

tests/consistent_id_mappings.rs

@@ -0,0 +1,16 @@
+use birdcage::{Birdcage, Sandbox};
+
+fn main() {
+    let uid = unsafe { libc::getuid() };
+    let gid = unsafe { libc::getgid() };
+    let euid = unsafe { libc::geteuid() };
+    let egid = unsafe { libc::getegid() };
+
+    let birdcage = Birdcage::new().unwrap();
+    birdcage.lock().unwrap();
+
+    assert_eq!(uid, unsafe { libc::getuid() });
+    assert_eq!(gid, unsafe { libc::getgid() });
+    assert_eq!(euid, unsafe { libc::geteuid() });
+    assert_eq!(egid, unsafe { libc::getegid() });
+}