Make the SendTarget trait a public trait (#633)

crates/core/src/test/mod.rs

@@ -4,5 +4,5 @@ mod client;
 mod request;
 mod response;
 pub use client::TestClient;
-pub use request::RequestBuilder;
+pub use request::{RequestBuilder, SendTarget};
 pub use response::ResponseExt;

crates/core/src/test/request/builder.rs

@@ -247,8 +247,11 @@ impl RequestBuilder {
         target.call(self.build()).await
     }
 }
+
+/// Trait for sending request to target, such as [`Router`], [`Service`], [`Handler`]. for test usage.
 #[async_trait]
 pub trait SendTarget {
+    /// Send request to target, such as [`Router`], [`Service`], [`Handler`].
     #[must_use = "future must be used"]
     async fn call(self, req: Request) -> Response;
 }

crates/core/src/test/request/mod.rs

@@ -1,3 +1,3 @@
 mod builder;
 
-pub use builder::RequestBuilder;
+pub use builder::{RequestBuilder, SendTarget};