Merge pull request #20851 from englishm/patch-1

Docs: Should be `assert_eq!` not `assert_eq`

Reviewed-by: sfackler

Author: bors

src/doc/trpl/testing.md

@@ -309,7 +309,7 @@ extern crate adder;
 
 #[test]
 fn it_works() {
-    assert_eq(4, adder::add_two(2));
+    assert_eq!(4, adder::add_two(2));
 }   
 ```