Add more tests for future::and_then

Author: kpp

src/future.rs

@@ -181,14 +181,23 @@ mod tests {
     }
 
     #[test]
-    fn test_and_then() {
+    fn test_and_then_ok() {
         executor::block_on(async {
             let future = ready(Ok::<i32, i32>(1));
             let new_future = and_then(future, |x| ready(Ok::<i32, i32>(x + 3)));
             assert_eq!(new_future.await, Ok(4));
         });
     }
 
+    #[test]
+    fn test_and_then_err() {
+        executor::block_on(async {
+            let future = ready(Err::<i32, i32>(1));
+            let new_future = and_then(future, |x| ready(Ok::<i32, i32>(x + 3)));
+            assert_eq!(new_future.await, Err(1));
+        });
+    }
+
     #[test]
     fn test_or_else() {
         executor::block_on(async {