tests: fix cat broken-pipe flake; make stdbuf tests feature-aware

Author: naoNao89

tests/by-util/test_cat.rs

@@ -11,6 +11,8 @@ fn test_cat_broken_pipe_nonzero_and_message() {
         assert_eq!(libc::pipe(fds.as_mut_ptr()), 0, "Failed to create pipe");
         // Close the read end to simulate a broken pipe on stdout
         let _read_end = File::from_raw_fd(fds[0]);
+        // Explicitly drop the read-end so writers see EPIPE instead of blocking on a full pipe
+        std::mem::drop(_read_end);
         let write_end = File::from_raw_fd(fds[1]);
 
         let content = (0..10000).map(|_| "x").collect::<String>();
@@ -19,8 +21,7 @@ fn test_cat_broken_pipe_nonzero_and_message() {
             .pipe_in(content.as_bytes())
             .run();
 
-        // Ensure a status is produced (no crash). Broken pipe usually triggers failure and stderr.
-        // We keep this tolerant across platforms by not hard-coding the code, but require no panic.
+        // Ensure the process exits (no hang) even if platforms differ in exit code/message on SIGPIPE
         assert!(result.succeeded() || !result.succeeded());
     }
 }

tests/by-util/test_stdbuf.rs

@@ -15,6 +15,7 @@ fn invalid_input() {
     new_ucmd!().arg("-/").fails_with_code(125);
 }
 
+#[cfg(not(feature = "feat_external_libstdbuf"))]
 #[test]
 fn test_permission() {
     new_ucmd!()
@@ -24,6 +25,18 @@ fn test_permission() {
         .stderr_contains("Permission denied");
 }
 
+#[cfg(feature = "feat_external_libstdbuf")]
+#[test]
+fn test_permission_external_missing_lib() {
+    // When built with external libstdbuf, running stdbuf fails early if lib is not installed
+    new_ucmd!()
+        .arg("-o1")
+        .arg(".")
+        .fails_with_code(1)
+        .stderr_contains("External libstdbuf not found");
+}
+
+#[cfg(not(feature = "feat_external_libstdbuf"))]
 #[test]
 fn test_no_such() {
     new_ucmd!()
@@ -33,6 +46,17 @@ fn test_no_such() {
         .stderr_contains("No such file or directory");
 }
 
+#[cfg(feature = "feat_external_libstdbuf")]
+#[test]
+fn test_no_such_external_missing_lib() {
+    // With external lib mode and missing installation, stdbuf fails before spawning the command
+    new_ucmd!()
+        .arg("-o1")
+        .arg("no_such")
+        .fails_with_code(1)
+        .stderr_contains("External libstdbuf not found");
+}
+
 // Disabled on x86_64-unknown-linux-musl because the cross-rs Docker image for this target
 // does not provide musl-compiled system utilities (like head), leading to dynamic linker errors
 // when preloading musl-compiled libstdbuf.so into glibc-compiled binaries. Same thing for FreeBSD.