test(stream): lock canonical delta semantics

Author: loong10k

src/test/java/io/github/easy4j/opencode/api/OpenCodeChatClientStreamingContractTest.java

@@ -0,0 +1,68 @@
+package io.github.easy4j.opencode.api;
+
+import io.github.easy4j.opencode.OpenCodeHttpClientConfig;
+import io.github.easy4j.opencode.api.sse.SseEvent;
+import io.github.easy4j.opencode.api.sse.StreamingChatResponse;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Method;
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class OpenCodeChatClientStreamingContractTest {
+
+    @Test
+    void messagePartDeltaMustAppendTextExactlyOnce() throws Exception {
+        OpenCodeChatClient client = new OpenCodeChatClient(new OpenCodeHttpClientConfig());
+        try {
+            StreamingChatResponse stream = new StreamingChatResponse();
+            SseEvent event = event("message.part.delta", "sess-1");
+            event.getProperties().put("field", "text");
+            event.getProperties().put("delta", "hello");
+
+            invokeHandleEvent(client, "sess-1", event, stream);
+
+            assertEquals("hello", stream.getAccumulatedContent());
+        } finally {
+            client.close();
+        }
+    }
+
+    @Test
+    void messagePartUpdatedSnapshotMustNotBeAppendedAsDelta() throws Exception {
+        OpenCodeChatClient client = new OpenCodeChatClient(new OpenCodeHttpClientConfig());
+        try {
+            StreamingChatResponse stream = new StreamingChatResponse();
+            SseEvent event = event("message.part.updated", "sess-1");
+            Map<String, Object> part = new HashMap<String, Object>();
+            part.put("type", "text");
+            part.put("text", "whole snapshot");
+            event.getProperties().put("part", part);
+
+            invokeHandleEvent(client, "sess-1", event, stream);
+
+            assertEquals("", stream.getAccumulatedContent());
+        } finally {
+            client.close();
+        }
+    }
+
+    private static SseEvent event(String type, String sessionId) {
+        SseEvent event = new SseEvent();
+        event.setType(type);
+        Map<String, Object> properties = new HashMap<String, Object>();
+        properties.put("sessionID", sessionId);
+        event.setProperties(properties);
+        return event;
+    }
+
+    private static void invokeHandleEvent(OpenCodeChatClient client, String sessionId,
+                                          SseEvent event, StreamingChatResponse stream) throws Exception {
+        Method method = OpenCodeChatClient.class.getDeclaredMethod(
+                "handleEvent", String.class, SseEvent.class, StreamingChatResponse.class);
+        method.setAccessible(true);
+        method.invoke(client, sessionId, event, stream);
+    }
+}