Fix already_failing_tests_are_detected_before_running_mutants

The test failure error message changed slightly on nightly to include the thread id, which broke the
test assertions.

Author: sourcefrog

NEWS.md

@@ -1,5 +1,9 @@
 # cargo-mutants changelog
 
+## 25.3.1 2025-08-10
+
+- Fixed: cargo-mutants' own tests were failing on nightly due to a change in the format of messages emitted by tests.
+
 ## 25.3.0 2025-08-10
 
 - New: A specific clearer error if a valid non-empty diff changes no Rust source files, and so matches no mutants. Thanks to @brunoerg.

tests/main.rs

@@ -618,7 +618,7 @@ fn already_failing_tests_are_detected_before_running_mutants() {
         .stdout(
             predicate::str::contains("running 1 test\ntest test_factorial ... FAILED")
                 .normalize()
-                .and(predicate::str::contains("thread 'test_factorial' panicked"))
+                .and(predicate::str::contains("assertion `left == right` failed"))
                 .and(predicate::str::contains("72")) // the failing value should be in the output
                 .and(predicate::str::contains("lib.rs:11:5"))
                 .and(