[gemini] Add test for parallel function call request reconstruction

The batch JSON helpers were covered by unit tests, but the request shape
that actually fixes the parallel call rejection was not. Add a test that
drives sendPrompt() with a two-call batch history, captures the
serialized request body and asserts that it contains one model content
with both functionCall parts followed by one user content with both
matching functionResponse parts, preserving the first call's
thoughtSignature and both call ids.

A second test covers the legacy single-call message format to make sure
conversations stored by earlier versions still replay and that absent
call ids are omitted from the request.

Signed-off-by: Christian Heldt <snaut@tutanota.com>

Author: cheldt

bundles/org.openhab.binding.gemini/src/test/java/org/openhab/binding/gemini/internal/api/GeminiApiClientTest.java

@@ -0,0 +1,205 @@
+/*
+ * Copyright (c) 2010-2026 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.binding.gemini.internal.api;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyLong;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.concurrent.TimeUnit;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jetty.client.HttpClient;
+import org.eclipse.jetty.client.api.ContentProvider;
+import org.eclipse.jetty.client.api.ContentResponse;
+import org.eclipse.jetty.client.api.Request;
+import org.eclipse.jetty.http.HttpHeader;
+import org.eclipse.jetty.http.HttpMethod;
+import org.eclipse.jetty.http.HttpStatus;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentCaptor;
+import org.openhab.core.voice.text.conversation.Conversation;
+import org.openhab.core.voice.text.conversation.ConversationRole;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+/**
+ * Tests for the request reconstruction of {@link GeminiApiClient}, i.e. how a stored conversation
+ * history is turned back into the {@code contents} of a Gemini {@code generateContent} request.
+ *
+ * <p>
+ * The parallel function call case is the behaviour that must not regress: all calls of one batch have
+ * to be replayed as the parts of a single model turn, followed by a single user turn holding all
+ * function responses. Splitting them into separate turns makes Gemini 3.x reject the request with
+ * {@code 400 INVALID_ARGUMENT} because only the first call carries a thought signature.
+ *
+ * @author Christian Heldt - Initial contribution
+ */
+@NonNullByDefault
+public class GeminiApiClientTest {
+
+    private static final String MODEL = "gemini-3.5-flash-lite";
+    private static final String PROMPT = "Which lamps in the living room are on?";
+    private static final String RESPONSE_JSON = """
+            {"candidates":[{"content":{"role":"model","parts":[{"text":"Lamp1 is on."}]}}]}""";
+
+    private final ObjectMapper objectMapper = new ObjectMapper();
+
+    private @NonNullByDefault({}) HttpClient httpClient;
+    private @NonNullByDefault({}) Request request;
+    private @NonNullByDefault({}) ContentResponse response;
+    private @NonNullByDefault({}) GeminiApiClient apiClient;
+
+    private static <T> T typedMock(Class<T> clazz) {
+        return Objects.requireNonNull(mock(clazz));
+    }
+
+    @BeforeEach
+    public void setUp() throws Exception {
+        httpClient = typedMock(HttpClient.class);
+        request = typedMock(Request.class);
+        response = typedMock(ContentResponse.class);
+
+        when(httpClient.newRequest(anyString())).thenReturn(request);
+        when(request.method(any(HttpMethod.class))).thenReturn(request);
+        when(request.timeout(anyLong(), any(TimeUnit.class))).thenReturn(request);
+        when(request.header(any(HttpHeader.class), anyString())).thenReturn(request);
+        when(request.header(anyString(), anyString())).thenReturn(request);
+        when(request.content(any(ContentProvider.class))).thenReturn(request);
+        when(request.send()).thenReturn(response);
+        when(response.getStatus()).thenReturn(HttpStatus.OK_200);
+        when(response.getContentAsString()).thenReturn(RESPONSE_JSON);
+
+        apiClient = new GeminiApiClient(httpClient, "test-api-key");
+    }
+
+    @Test
+    public void parallelToolCallsAreSerializedAsOneModelTurnAndOneUserTurn() throws Exception {
+        // Gemini sends parallel calls as one model turn and puts the thought signature on the first part only
+        List<GeminiLLMToolCall> calls = List.of(
+                new GeminiLLMToolCall("item-get-state", Map.of("item", "Lamp1"), "call-1", "signature-abc"),
+                new GeminiLLMToolCall("item-get-state", Map.of("item", "Lamp2"), "call-2", null));
+        List<Conversation.Message> history = List.of(new Conversation.Message(1, ConversationRole.USER, PROMPT),
+                new Conversation.Message(2, ConversationRole.TOOL_CALL, GeminiLLMToolCall.toJsonList(calls)),
+                new Conversation.Message(3, ConversationRole.TOOL_RETURN,
+                        GeminiLLMToolCall.resultsToJson(List.of("Lamp1 is ON", "Lamp2 is OFF"))));
+
+        apiClient.sendPrompt(MODEL, history, List.of(), null, null, null, null, null);
+
+        JsonNode contents = captureRequestBody().get("contents");
+        // one user turn, one model turn with both calls, one user turn with both responses - a split
+        // into per-call turns would yield four contents here
+        assertEquals(3, contents.size());
+
+        JsonNode userTurn = contents.get(0);
+        assertEquals("user", userTurn.get("role").asText());
+        assertEquals(PROMPT, userTurn.get("parts").get(0).get("text").asText());
+
+        JsonNode callTurn = contents.get(1);
+        assertEquals("model", callTurn.get("role").asText());
+        JsonNode callParts = callTurn.get("parts");
+        assertEquals(2, callParts.size());
+
+        JsonNode firstCallPart = callParts.get(0);
+        assertFalse(firstCallPart.has("text"));
+        assertEquals("signature-abc", firstCallPart.get("thoughtSignature").asText());
+        JsonNode firstCall = firstCallPart.get("functionCall");
+        assertEquals("item-get-state", firstCall.get("name").asText());
+        assertEquals("Lamp1", firstCall.get("args").get("item").asText());
+        assertEquals("call-1", firstCall.get("id").asText());
+
+        JsonNode secondCallPart = callParts.get(1);
+        assertFalse(secondCallPart.has("text"));
+        // Gemini only signs the first part of a batch, so the second one must not carry a signature
+        assertFalse(secondCallPart.has("thoughtSignature"));
+        JsonNode secondCall = secondCallPart.get("functionCall");
+        assertEquals("item-get-state", secondCall.get("name").asText());
+        assertEquals("Lamp2", secondCall.get("args").get("item").asText());
+        assertEquals("call-2", secondCall.get("id").asText());
+
+        JsonNode returnTurn = contents.get(2);
+        assertEquals("user", returnTurn.get("role").asText());
+        JsonNode returnParts = returnTurn.get("parts");
+        assertEquals(2, returnParts.size());
+
+        // the results are paired with the calls by position, and the call id is echoed so that
+        // equally named parallel calls can be told apart
+        JsonNode firstResponse = returnParts.get(0).get("functionResponse");
+        assertEquals("item-get-state", firstResponse.get("name").asText());
+        assertEquals("call-1", firstResponse.get("id").asText());
+        assertEquals("Lamp1 is ON", firstResponse.get("response").get("result").asText());
+
+        JsonNode secondResponse = returnParts.get(1).get("functionResponse");
+        assertEquals("item-get-state", secondResponse.get("name").asText());
+        assertEquals("call-2", secondResponse.get("id").asText());
+        assertEquals("Lamp2 is OFF", secondResponse.get("response").get("result").asText());
+    }
+
+    @Test
+    public void singleToolCallUsesLegacyMessageFormatAndOmitsAbsentIds() throws Exception {
+        // conversations stored by earlier versions hold a single call as a JSON object and its result as plain text
+        GeminiLLMToolCall call = new GeminiLLMToolCall("item-get-state", Map.of("item", "Lamp1"), null, null);
+        List<Conversation.Message> history = List.of(new Conversation.Message(1, ConversationRole.USER, PROMPT),
+                new Conversation.Message(2, ConversationRole.TOOL_CALL, call.toJson()),
+                new Conversation.Message(3, ConversationRole.TOOL_RETURN, "Lamp1 is ON"));
+
+        apiClient.sendPrompt(MODEL, history, List.of(), null, null, null, null, null);
+
+        JsonNode contents = captureRequestBody().get("contents");
+        assertEquals(3, contents.size());
+
+        JsonNode callParts = contents.get(1).get("parts");
+        assertEquals("model", contents.get(1).get("role").asText());
+        assertEquals(1, callParts.size());
+        assertFalse(callParts.get(0).has("thoughtSignature"));
+        JsonNode functionCall = callParts.get(0).get("functionCall");
+        assertEquals("item-get-state", functionCall.get("name").asText());
+        assertEquals("Lamp1", functionCall.get("args").get("item").asText());
+        // no id was stored, so none must be sent
+        assertFalse(functionCall.has("id"));
+
+        JsonNode returnParts = contents.get(2).get("parts");
+        assertEquals("user", contents.get(2).get("role").asText());
+        assertEquals(1, returnParts.size());
+        JsonNode functionResponse = returnParts.get(0).get("functionResponse");
+        assertEquals("item-get-state", functionResponse.get("name").asText());
+        assertEquals("Lamp1 is ON", functionResponse.get("response").get("result").asText());
+        assertFalse(functionResponse.has("id"));
+    }
+
+    private JsonNode captureRequestBody() throws Exception {
+        ArgumentCaptor<ContentProvider> captor = ArgumentCaptor.forClass(ContentProvider.class);
+        verify(request).content(captor.capture());
+
+        StringBuilder body = new StringBuilder();
+        for (ByteBuffer buffer : Objects.requireNonNull(captor.getValue())) {
+            body.append(StandardCharsets.UTF_8.decode(buffer));
+        }
+        JsonNode root = objectMapper.readTree(body.toString());
+        assertTrue(root.has("contents"), "request payload has no contents");
+        return root;
+    }
+}