Update test

tests/ui/unnecessary_flat_map.fixed

@@ -1,13 +1,14 @@
 // run-rustfix
 
+#![allow(unused_imports)]
 #![warn(clippy::flat_map_identity)]
 
 use std::convert;
 
 fn main() {
     let iterator = [[0, 1], [2, 3], [4, 5]].iter();
-    iterator.flatten();
+    let _ = iterator.flatten();
 
     let iterator = [[0, 1], [2, 3], [4, 5]].iter();
-    iterator.flatten();
+    let _ = iterator.flatten();
 }

tests/ui/unnecessary_flat_map.rs

@@ -1,13 +1,14 @@
 // run-rustfix
 
+#![allow(unused_imports)]
 #![warn(clippy::flat_map_identity)]
 
 use std::convert;
 
 fn main() {
     let iterator = [[0, 1], [2, 3], [4, 5]].iter();
-    iterator.flat_map(|x| x);
+    let _ = iterator.flat_map(|x| x);
 
     let iterator = [[0, 1], [2, 3], [4, 5]].iter();
-    iterator.flat_map(convert::identity);
+    let _ = iterator.flat_map(convert::identity);
 }

tests/ui/unnecessary_flat_map.stderr

@@ -1,16 +1,16 @@
 error: called `flat_map(|x| x)` on an `Iterator`
-  --> $DIR/unnecessary_flat_map.rs:9:14
+  --> $DIR/unnecessary_flat_map.rs:10:22
    |
-LL |     iterator.flat_map(|x| x);
-   |              ^^^^^^^^^^^^^^^ help: try: `flatten()`
+LL |     let _ = iterator.flat_map(|x| x);
+   |                      ^^^^^^^^^^^^^^^ help: try: `flatten()`
    |
    = note: `-D clippy::flat-map-identity` implied by `-D warnings`
 
 error: called `flat_map(std::convert::identity)` on an `Iterator`
-  --> $DIR/unnecessary_flat_map.rs:12:14
+  --> $DIR/unnecessary_flat_map.rs:13:22
    |
-LL |     iterator.flat_map(convert::identity);
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `flatten()`
+LL |     let _ = iterator.flat_map(convert::identity);
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `flatten()`
 
 error: aborting due to 2 previous errors