give each appservice test its own scratch directory

swarm-matrix-ctl/src/appservice.rs

@@ -447,15 +447,16 @@ mod tests {
 
     const REGEX: &str = "^@[a-z0-9._=/-]+:t\\.local$";
 
+    /// A directory of its own per call. A counter, not the clock, keeps two
+    /// tests that start in the same clock tick out of one directory.
     fn scratch() -> PathBuf {
+        static NEXT: std::sync::atomic::AtomicU32 = std::sync::atomic::AtomicU32::new(0);
         let dir = std::env::temp_dir().join(format!(
             "swarm-appservice-{}-{}",
             std::process::id(),
-            std::time::SystemTime::now()
-                .duration_since(std::time::UNIX_EPOCH)
-                .expect("after the epoch")
-                .as_nanos()
+            NEXT.fetch_add(1, std::sync::atomic::Ordering::Relaxed)
         ));
+        std::fs::remove_dir_all(&dir).ok();
         std::fs::create_dir_all(&dir).expect("temp dir");
         dir
     }