Mention in the readme that sync enables the

global singleton for the MockClock across all threads

README.md

@@ -59,4 +59,10 @@ MockClock::advance_system_time(Duration::from_secs(2));
 assert_eq!(now.elapsed().unwrap(), Duration::from_secs(17));
 ```
 
+# Caveats
+
+If the `sync` feature is enabled then all tests using this crate will use a global singleton clock.
+
+see <https://github.com/museun/mock_instant/issues/6>
+
 License: 0BSD

src/lib.rs

@@ -9,6 +9,10 @@ mock_instant = { version = "0.2", features = ["sync"] }
 
 It provides a replacement `std::time::Instant` and `std::time::SystemTime` that uses a deterministic thread-local 'clock'
 
+**NOTE:** if this is enabled then all tests will use the same singleton `MockClock` source
+
+---
+
 You can swap out the `std::time::Instant` with this one by doing something similar to:
 ```rust
 #[cfg(test)]