Reproduce #14076

The `with_stderr_contains()` (as well as the new `with_stderr_data()` too, see #14060) has no effect when using with `run_expect_error()`.

Author: choznerol

tests/testsuite/check_cfg.rs

@@ -632,7 +632,9 @@ fn config_invalid_empty() {
         .build();
 
     p.cargo("check")
-        .with_stderr_contains("[..]missing field `level`[..]")
+        .with_stderr_contains(
+            "[..]missing field `level`[..] THIS RANDOM SENTENCE SHOULD FAIL THIS TEST BUT DIDN'T",
+        )
         .run_expect_error();
 }
 

tests/testsuite/freshness.rs

@@ -2936,6 +2936,9 @@ fn use_mtime_cache_in_cargo_home() {
         .with_stderr(
             "\
 [DIRTY] foo v0.5.0 ([CWD]): [..]
+
+    THIS RANDOM SENTENCE SHOULD FAIL THIS TEST BUT DIDN'T
+
 [CHECKING] foo v0.5.0 ([CWD])
 [RUNNING] `rustc --crate-name foo --edition=2015 src/lib.rs [..]",
         )