mock: document public APIs in event module

tracing-mock/Cargo.toml

@@ -20,7 +20,7 @@ publish = false
 [dependencies]
 tracing = { path = "../tracing", version = "0.2" }
 tracing-core = { path = "../tracing-core", version = "0.2", default-features = false }
-tracing-subscriber = { path = "../tracing-subscriber", version = "0.3", default-features = false, optional = true }
+tracing-subscriber = { path = "../tracing-subscriber", version = "0.3", default-features = false, features = ["registry"], optional = true }
 tokio-test = { version = "0.4.2", optional = true }
 
 # Fix minimal-versions; tokio-test fails with otherwise acceptable 0.1.0

tracing-mock/src/collector.rs

@@ -229,6 +229,14 @@ where
         match self.expected.lock().unwrap().pop_front() {
             None => {}
             Some(Expect::Event(mut expected)) => {
+                #[cfg(feature = "tracing-subscriber")]
+                {
+                    if !expected.scope_mut().is_empty() {
+                        unimplemented!(
+                            "Expected scope for events is not supported with `MockCollector`."
+                        )
+                    }
+                }
                 let get_parent_name = || {
                     let stack = self.current.lock().unwrap();
                     let spans = self.spans.lock().unwrap();