test(ffi): assert cdylib exists and is readable before ELF inspection

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: yannham

libdd-otel-thread-ctx-ffi/tests/elf_properties.rs

@@ -21,19 +21,34 @@ fn cdylib_path() -> PathBuf {
     PathBuf::from(env!("CDYLIB_PROFILE_DIR")).join("liblibdd_otel_thread_ctx_ffi.so")
 }
 
+fn check_cdylib_exists(path: &PathBuf) {
+    assert!(
+        path.exists(),
+        "cdylib not found at {}: \
+         ensure `cargo build -p libdd-otel-thread-ctx-ffi` has been run for this profile",
+        path.display()
+    );
+    assert!(
+        std::fs::File::open(path).is_ok(),
+        "cdylib exists at {} but could not be opened for reading",
+        path.display()
+    );
+}
+
 fn readelf(args: &[&str], path: &PathBuf) -> String {
     let out = Command::new("readelf")
         .args(args)
         .arg(path)
         .output()
-        .expect("failed to run readelf — is binutils installed?");
+        .expect("failed to run readelf. Is binutils installed?");
     String::from_utf8_lossy(&out.stdout).into_owned()
 }
 
 #[test]
 #[cfg_attr(miri, ignore)]
 fn otel_thread_ctx_v1_in_dynsym() {
     let path = cdylib_path();
+    check_cdylib_exists(&path);
     let output = readelf(&["-W", "--dyn-syms"], &path);
     let line = output
         .lines()
@@ -49,6 +64,7 @@ fn otel_thread_ctx_v1_in_dynsym() {
 #[cfg_attr(miri, ignore)]
 fn otel_thread_ctx_v1_tlsdesc_reloc() {
     let path = cdylib_path();
+    check_cdylib_exists(&path);
     let output = readelf(&["-W", "--relocs"], &path);
     let found = output.lines().any(|l| {
         l.contains(SYMBOL) && (l.contains("R_X86_64_TLSDESC") || l.contains("R_AARCH64_TLSDESC"))