agent: fix race condition when test watcher

create_tmpfs won't pass as the race condition in watcher umount. quote
James's words here:

1. Rust runs all tests in parallel.
2. Mounts are a process-wide, not a per-thread resource.
The only test that calls watcher.mount() is create_tmpfs().
However, other tests create BindWatcher objects.
3. BindWatcher's drop() implementation calls self.cleanup(),
which calls unmount for the mountpoint create_tmpfs() asserts.
4. The other tests are calling unmount whenever a BindWatcher goes
out of scope.

To avoid that issue, let the tests using BindWatcher in watcher and
sandbox.rs run sequentially.

Fixes: #2809
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>

src/agent/Cargo.lock

@@ -545,6 +545,7 @@ dependencies = [
  "scan_fmt",
  "scopeguard",
  "serde_json",
+ "serial_test",
  "slog",
  "slog-scope",
  "slog-stdlog",

src/agent/Cargo.toml

@@ -20,6 +20,7 @@ scan_fmt = "0.2.3"
 scopeguard = "1.0.0"
 thiserror = "1.0.26"
 regex = "1"
+serial_test = "0.5.1"
 
 # Async helpers
 async-trait = "0.1.42"

src/agent/src/sandbox.rs

@@ -465,7 +465,10 @@ mod tests {
         baremount.mount()
     }
 
+    use serial_test::serial;
+
     #[tokio::test]
+    #[serial]
     async fn set_sandbox_storage() {
         let logger = slog::Logger::root(slog::Discard, o!());
         let mut s = Sandbox::new(&logger).unwrap();
@@ -500,6 +503,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn remove_sandbox_storage() {
         skip_if_not_root!();
 
@@ -556,6 +560,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn unset_and_remove_sandbox_storage() {
         skip_if_not_root!();
 
@@ -607,6 +612,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn unset_sandbox_storage() {
         let logger = slog::Logger::root(slog::Discard, o!());
         let mut s = Sandbox::new(&logger).unwrap();
@@ -690,6 +696,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn get_container_entry_exist() {
         skip_if_not_root!();
         let logger = slog::Logger::root(slog::Discard, o!());
@@ -703,6 +710,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn get_container_no_entry() {
         let logger = slog::Logger::root(slog::Discard, o!());
         let mut s = Sandbox::new(&logger).unwrap();
@@ -712,6 +720,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn add_and_get_container() {
         skip_if_not_root!();
         let logger = slog::Logger::root(slog::Discard, o!());
@@ -723,6 +732,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn update_shared_pidns() {
         skip_if_not_root!();
         let logger = slog::Logger::root(slog::Discard, o!());
@@ -741,6 +751,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn add_guest_hooks() {
         let logger = slog::Logger::root(slog::Discard, o!());
         let mut s = Sandbox::new(&logger).unwrap();
@@ -764,6 +775,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn test_sandbox_set_destroy() {
         let logger = slog::Logger::root(slog::Discard, o!());
         let mut s = Sandbox::new(&logger).unwrap();

src/agent/src/watcher.rs

@@ -982,7 +982,10 @@ mod tests {
         );
     }
 
+    use serial_test::serial;
+
     #[tokio::test]
+    #[serial]
     async fn create_tmpfs() {
         skip_if_not_root!();
 
@@ -997,6 +1000,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn spawn_thread() {
         skip_if_not_root!();
 
@@ -1026,6 +1030,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[serial]
     async fn verify_container_cleanup_watching() {
         skip_if_not_root!();