Include multiple cases generating correct return code

cargo.out

@@ -1,22 +1,22 @@
    Compiling futuretest v0.1.0 (file:///mnt/c/Users/Mahmoud/git/futuretest)
 error[E0271]: type mismatch resolving `<futures::FutureResult<(), std::string::String> as futures::IntoFuture>::Error == &str`
-  --> src/main.rs:12:10
+  --> src/main.rs:13:10
    |
-12 |         .and_then(|_|
+13 |         .and_then(|_|
    |          ^^^^^^^^ expected struct `std::string::String`, found &str
    |
    = note: expected type `std::string::String`
               found type `&str`
 
 error[E0271]: type mismatch resolving `<futures::FutureResult<(), std::string::String> as futures::IntoFuture>::Error == &str`
-  --> src/main.rs:19:10
+  --> src/main.rs:20:10
    |
-19 |     core.run(f).unwrap();
+20 |     core.run(f).unwrap();
    |          ^^^ expected struct `std::string::String`, found &str
    |
    = note: expected type `std::string::String`
               found type `&str`
-   = note: required because of the requirements on the impl of `futures::Future` for `futures::AndThen<futures::MapErr<futures::FutureResult<(), ()>, [closure@src/main.rs:11:18: 11:43]>, futures::FutureResult<(), std::string::String>, [closure@src/main.rs:12:19: 15:14]>`
+   = note: required because of the requirements on the impl of `futures::Future` for `futures::AndThen<futures::Map<futures::MapErr<futures::FutureResult<(), ()>, [closure@src/main.rs:11:18: 11:43]>, [closure@src/main.rs:12:14: 12:67]>, futures::FutureResult<(), std::string::String>, [closure@src/main.rs:13:19: 16:14]>`
 
 error: aborting due to 2 previous errors
 

src/main.rs

@@ -9,6 +9,7 @@ fn main() {
 
     let f = future::result(Ok(()))
         .map_err(|()| "&'static str error")
+        .map(|_| future::result(Err("another &'static str error")))
         .and_then(|_|
              future::result(Ok(())
                 .map_err(|()| "String error".to_owned())