From f41ffb08ec2dc80538460a7b333b8195d9378d99 Mon Sep 17 00:00:00 2001
From: Andrew Lamb <andrew@nerdnetworks.org>
Date: Fri, 23 Jan 2026 20:35:07 -0500
Subject: [PATCH] Add additional test coverage

---
 arrow-avro/src/writer/encoder.rs | 46 ++++++++++++++++++++++++++++++++
 arrow-avro/src/writer/format.rs  | 44 ++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)

diff --git a/arrow-avro/src/writer/encoder.rs b/arrow-avro/src/writer/encoder.rs
index 97825b1bd895..a53e540de9b0 100644
--- a/arrow-avro/src/writer/encoder.rs
+++ b/arrow-avro/src/writer/encoder.rs
@@ -3380,4 +3380,50 @@ mod tests {
         expected_row2.extend(avro_long_bytes(3)); // value
         assert_bytes_eq(row_slice(&out, &offsets, 2), &expected_row2);
     }
+
+    #[test]
+    fn encode_prefix_write_error() {
+        use crate::codec::AvroFieldBuilder;
+        use crate::schema::{AvroSchema, FingerprintAlgorithm};
+        use std::io;
+
+        struct FailWriter {
+            failed: bool,
+        }
+
+        impl io::Write for FailWriter {
+            fn write(&mut self, _buf: &[u8]) -> io::Result<usize> {
+                if !self.failed {
+                    self.failed = true;
+                    Err(io::Error::new(io::ErrorKind::Other, "fail write"))
+                } else {
+                    Ok(0)
+                }
+            }
+
+            fn flush(&mut self) -> io::Result<()> {
+                Ok(())
+            }
+        }
+
+        let schema = ArrowSchema::new(vec![Field::new("x", DataType::Int32, false)]);
+        let arr = Int32Array::from(vec![42]);
+        let batch = RecordBatch::try_new(Arc::new(schema.clone()), vec![Arc::new(arr)]).unwrap();
+        let avro_schema = AvroSchema::try_from(&schema).unwrap();
+        let fingerprint = avro_schema
+            .fingerprint(FingerprintAlgorithm::Rabin)
+            .unwrap();
+        let avro_root = AvroFieldBuilder::new(&avro_schema.schema().unwrap())
+            .build()
+            .unwrap();
+        let encoder = RecordEncoderBuilder::new(&avro_root, &schema)
+            .with_fingerprint(Some(fingerprint))
+            .build()
+            .unwrap();
+
+        let mut writer = FailWriter { failed: false };
+        let err = encoder.encode(&mut writer, &batch).unwrap_err();
+        let msg = format!("{err}");
+        assert!(msg.contains("write prefix"), "unexpected error: {msg}");
+    }
 }
diff --git a/arrow-avro/src/writer/format.rs b/arrow-avro/src/writer/format.rs
index b8d69787b03c..9abb8755ab8c 100644
--- a/arrow-avro/src/writer/format.rs
+++ b/arrow-avro/src/writer/format.rs
@@ -169,6 +169,50 @@ impl AvroFormat for AvroBinaryFormat {
     }
 }
 
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use arrow_schema::{DataType, Field, Schema};
+
+    fn test_schema() -> Schema {
+        Schema::new(vec![Field::new("x", DataType::Int32, false)])
+    }
+
+    #[test]
+    fn avro_binary_format_rejects_compression() {
+        let mut format = AvroBinaryFormat::default();
+        let schema = test_schema();
+        let err = format
+            .start_stream(
+                &mut Vec::<u8>::new(),
+                &schema,
+                Some(CompressionCodec::Snappy),
+            )
+            .unwrap_err();
+        assert!(
+            err.to_string()
+                .contains("Compression not supported for Avro binary streaming")
+        );
+    }
+
+    #[test]
+    fn avro_soe_format_rejects_compression() {
+        let mut format = AvroSoeFormat::default();
+        let schema = test_schema();
+        let err = format
+            .start_stream(
+                &mut Vec::<u8>::new(),
+                &schema,
+                Some(CompressionCodec::Snappy),
+            )
+            .unwrap_err();
+        assert!(
+            err.to_string()
+                .contains("Compression not supported for Avro SOE streaming")
+        );
+    }
+}
+
 #[inline]
 fn write_string<W: Write>(writer: &mut W, s: &str) -> Result<(), ArrowError> {
     write_bytes(writer, s.as_bytes())