test(compat-0.3): cover null part metadata conversions (#1289)

Add regression coverage for text and data metadata conversion and defensive copying. The runtime fix is already in #1261.

Related to #1275.

Signed-off-by: Japneet Singh <japneet.singh2024@gmail.com>

Author: Orcus01

compat-0.3/server-conversion/src/test/java/org/a2aproject/sdk/compat03/conversion/mappers/domain/NullData_v0_3_Test.java

@@ -8,8 +8,12 @@
 import java.util.Collections;
 import java.util.Map;
 import org.a2aproject.sdk.compat03.spec.DataPart_v0_3;
+import org.a2aproject.sdk.compat03.spec.Part_v0_3;
+import org.a2aproject.sdk.compat03.spec.TextPart_v0_3;
 import org.a2aproject.sdk.spec.DataPart;
 import org.a2aproject.sdk.spec.InvalidRequestError;
+import org.a2aproject.sdk.spec.Part;
+import org.a2aproject.sdk.spec.TextPart;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
@@ -31,6 +35,36 @@ void objectNullsSurviveBothConversionDirections() {
         assertEquals(original, PartMapper_v0_3.INSTANCE.toV10(legacy));
     }
 
+    @ParameterizedTest
+    @ValueSource(strings = {"text", "data"})
+    void partMetadataNullsSurviveBothConversionDirections(String kind) {
+        Map<String, Object> metadata = Collections.singletonMap("optional", null);
+        Map<String, Object> data = Map.of("value", "hello");
+        Part<?> current =
+                kind.equals("text")
+                        ? new TextPart("hello", metadata)
+                        : new DataPart(data, metadata);
+        Part_v0_3<?> legacy =
+                kind.equals("text")
+                        ? new TextPart_v0_3("hello", metadata)
+                        : new DataPart_v0_3(data, metadata);
+
+        Part_v0_3<?> downgraded = PartMapper_v0_3.INSTANCE.fromV10(current);
+        Part<?> upgraded = PartMapper_v0_3.INSTANCE.toV10(legacy);
+        assertEquals(legacy, downgraded);
+        assertEquals(current, upgraded);
+        assertEquals(
+                metadata,
+                kind.equals("text")
+                        ? assertInstanceOf(TextPart_v0_3.class, downgraded).metadata()
+                        : assertInstanceOf(DataPart_v0_3.class, downgraded).metadata());
+        assertEquals(
+                metadata,
+                kind.equals("text")
+                        ? assertInstanceOf(TextPart.class, upgraded).metadata()
+                        : assertInstanceOf(DataPart.class, upgraded).metadata());
+    }
+
     @ParameterizedTest
     @ValueSource(strings = {"null", "[]", "42", "true", "\"text\""})
     void nonObjectDataCannotBeDowngraded(String json) {

compat-0.3/spec/src/test/java/org/a2aproject/sdk/compat03/spec/NullValues_v0_3_Test.java

@@ -84,6 +84,22 @@ void dataObjectWithNullValuesIsDefensivelyCopied() {
         assertThrows(UnsupportedOperationException.class, () -> part.data().put("later", true));
     }
 
+    @ParameterizedTest
+    @ValueSource(strings = {"text", "data"})
+    void partMetadataWithNullValuesIsDefensivelyCopied(String kind) {
+        Map<String, Object> metadata = new HashMap<>();
+        metadata.put("optional", null);
+        Map<String, Object> copiedMetadata =
+                kind.equals("text")
+                        ? new TextPart_v0_3("hello", metadata).metadata()
+                        : new DataPart_v0_3(Map.of("value", "hello"), metadata).metadata();
+        metadata.put("optional", "changed");
+        metadata.put("later", true);
+
+        assertEquals(Collections.singletonMap("optional", null), copiedMetadata);
+        assertThrows(UnsupportedOperationException.class, () -> copiedMetadata.put("later", true));
+    }
+
     @Test
     void nullDataObjectRemainsInvalid() {
         assertThrows(IllegalArgumentException.class, () -> new DataPart_v0_3(null));