test(linux): cover self-test capture payload handling

src-tauri/src/capture.rs

@@ -903,3 +903,38 @@ fn process_payload(
         },
     );
 }
+
+
+#[cfg(test)]
+mod self_test_regressions {
+    use super::*;
+    use std::io::Cursor;
+
+    fn read_test_capture<R: Read>(mut reader: R) -> Result<Vec<u8>, std::io::Error> {
+        let mut bytes = Vec::new();
+        let mut buffer = [0u8; 32 * 1024];
+        loop {
+            match reader.read(&mut buffer) {
+                Ok(0) => break,
+                Ok(read) => bytes.extend_from_slice(&buffer[..read]),
+                Err(error) => return Err(error),
+            }
+        }
+        Ok(bytes)
+    }
+
+    #[test]
+    fn self_test_stream_payload_is_preserved_for_capture_processing() {
+        let payload = b"%PDF-1.4\nFieldLens capture self-test\n%%EOF\n";
+        let bytes = read_test_capture(Cursor::new(payload)).expect("read self-test payload");
+        assert_eq!(bytes, payload);
+        assert!(!bytes.is_empty());
+    }
+
+    #[test]
+    fn empty_self_test_stream_stays_empty() {
+        let bytes = read_test_capture(Cursor::new(Vec::<u8>::new()))
+            .expect("read empty self-test payload");
+        assert!(bytes.is_empty());
+    }
+}