PR #42541 on Rust is to make assert_eq error message be multi-line. Before implementing this we need to make the current test less brittle.
[FINISHED] release [optimized] target(s) in [..]
[RUNNING] target[/]release[/]deps[/]foo-[..][EXE]
thread '[..]' panicked at 'assertion failed: \
- `(left == right)` (left: \
- `\"hello\"`, right: `\"nope\"`)', src[/]foo.rs:14
-[..]
-", p.url()))
+ `(left == right)`", p.url()))
+ .with_stderr_contains("left: `\"hello\"`")
+ .with_stderr_contains("right: `\"nope\"`")
+ .with_stderr_contains("src[/]foo.rs:14")
.with_status(101));
}