diff --git a/spring-ai-model/src/test/java/org/springframework/ai/model/tool/DefaultToolExecutionResultTests.java b/spring-ai-model/src/test/java/org/springframework/ai/model/tool/DefaultToolExecutionResultTests.java
index c6c06c1e75e..947483cf374 100644
--- a/spring-ai-model/src/test/java/org/springframework/ai/model/tool/DefaultToolExecutionResultTests.java
+++ b/spring-ai-model/src/test/java/org/springframework/ai/model/tool/DefaultToolExecutionResultTests.java
@@ -17,6 +17,7 @@
 package org.springframework.ai.model.tool;
 
 import java.util.ArrayList;
+import java.util.List;
 
 import org.junit.jupiter.api.Test;
 
@@ -190,4 +191,34 @@ void whenEqualsAndHashCodeAreConsistent() {
 		assertThat(result1.hashCode()).isEqualTo(result2.hashCode());
 	}
 
+	@Test
+	void whenConversationHistoryIsImmutableList() {
+		List<Message> conversationHistory = List.of(new org.springframework.ai.chat.messages.UserMessage("Hello"),
+				new org.springframework.ai.chat.messages.UserMessage("Hi!"));
+
+		var result = DefaultToolExecutionResult.builder()
+			.conversationHistory(conversationHistory)
+			.returnDirect(false)
+			.build();
+
+		assertThat(result.conversationHistory()).hasSize(2);
+		assertThat(result.conversationHistory()).isEqualTo(conversationHistory);
+	}
+
+	@Test
+	void whenReturnDirectIsChangedMultipleTimes() {
+		var conversationHistory = new ArrayList<Message>();
+		conversationHistory.add(new org.springframework.ai.chat.messages.UserMessage("Test"));
+
+		var builder = DefaultToolExecutionResult.builder()
+			.conversationHistory(conversationHistory)
+			.returnDirect(true)
+			.returnDirect(false)
+			.returnDirect(true);
+
+		var result = builder.build();
+
+		assertThat(result.returnDirect()).isTrue();
+	}
+
 }
diff --git a/spring-ai-model/src/test/java/org/springframework/ai/model/tool/ToolExecutionEligibilityPredicateTests.java b/spring-ai-model/src/test/java/org/springframework/ai/model/tool/ToolExecutionEligibilityPredicateTests.java
index d347f9190f1..5cef425f942 100644
--- a/spring-ai-model/src/test/java/org/springframework/ai/model/tool/ToolExecutionEligibilityPredicateTests.java
+++ b/spring-ai-model/src/test/java/org/springframework/ai/model/tool/ToolExecutionEligibilityPredicateTests.java
@@ -16,6 +16,7 @@
 
 package org.springframework.ai.model.tool;
 
+import java.util.Collections;
 import java.util.List;
 
 import org.junit.jupiter.api.Test;
@@ -75,6 +76,32 @@ void whenTestMethodCalledDirectly() {
 		assertThat(result).isTrue();
 	}
 
+	@Test
+	void whenChatResponseHasEmptyGenerations() {
+		ToolExecutionEligibilityPredicate predicate = new TestToolExecutionEligibilityPredicate();
+		ChatOptions promptOptions = ChatOptions.builder().build();
+		ChatResponse emptyResponse = new ChatResponse(Collections.emptyList());
+
+		boolean result = predicate.isToolExecutionRequired(promptOptions, emptyResponse);
+		assertThat(result).isTrue();
+	}
+
+	@Test
+	void whenChatOptionsHasModel() {
+		ModelCheckingPredicate predicate = new ModelCheckingPredicate();
+
+		ChatOptions optionsWithModel = ChatOptions.builder().model("gpt-4").build();
+
+		ChatResponse chatResponse = new ChatResponse(List.of(new Generation(new AssistantMessage("test"))));
+
+		boolean result = predicate.isToolExecutionRequired(optionsWithModel, chatResponse);
+		assertThat(result).isTrue();
+
+		ChatOptions optionsWithoutModel = ChatOptions.builder().build();
+		result = predicate.isToolExecutionRequired(optionsWithoutModel, chatResponse);
+		assertThat(result).isFalse();
+	}
+
 	/**
 	 * Test implementation of {@link ToolExecutionEligibilityPredicate} that always
 	 * returns true.
@@ -88,4 +115,13 @@ public boolean test(ChatOptions promptOptions, ChatResponse chatResponse) {
 
 	}
 
+	private static class ModelCheckingPredicate implements ToolExecutionEligibilityPredicate {
+
+		@Override
+		public boolean test(ChatOptions promptOptions, ChatResponse chatResponse) {
+			return promptOptions.getModel() != null && !promptOptions.getModel().isEmpty();
+		}
+
+	}
+
 }
diff --git a/spring-ai-model/src/test/java/org/springframework/ai/model/tool/ToolExecutionResultTests.java b/spring-ai-model/src/test/java/org/springframework/ai/model/tool/ToolExecutionResultTests.java
index acb3bfca0c5..d7695b39ce7 100644
--- a/spring-ai-model/src/test/java/org/springframework/ai/model/tool/ToolExecutionResultTests.java
+++ b/spring-ai-model/src/test/java/org/springframework/ai/model/tool/ToolExecutionResultTests.java
@@ -25,6 +25,7 @@
 import org.springframework.ai.chat.messages.UserMessage;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.AssertionsForClassTypes.assertThatThrownBy;
 
 /**
  * Unit tests for {@link ToolExecutionResult}.
@@ -80,4 +81,63 @@ void whenMultipleToolCallsThenMultipleGenerations() {
 		assertThat(generations.get(1).getMetadata().getFinishReason()).isEqualTo(ToolExecutionResult.FINISH_REASON);
 	}
 
+	@Test
+	void whenEmptyConversationHistoryThenThrowsException() {
+		var toolExecutionResult = ToolExecutionResult.builder().conversationHistory(List.of()).build();
+
+		assertThatThrownBy(() -> ToolExecutionResult.buildGenerations(toolExecutionResult))
+			.isInstanceOf(ArrayIndexOutOfBoundsException.class);
+	}
+
+	@Test
+	void whenToolResponseWithEmptyResponseListThenEmptyGenerations() {
+		var toolExecutionResult = ToolExecutionResult.builder()
+			.conversationHistory(
+					List.of(new AssistantMessage("Processing request"), new ToolResponseMessage(List.of())))
+			.build();
+
+		var generations = ToolExecutionResult.buildGenerations(toolExecutionResult);
+
+		assertThat(generations).isEmpty();
+	}
+
+	@Test
+	void whenToolResponseWithNullContentThenGenerationWithNullText() {
+		var toolExecutionResult = ToolExecutionResult.builder()
+			.conversationHistory(
+					List.of(new ToolResponseMessage(List.of(new ToolResponseMessage.ToolResponse("1", "tool", null)))))
+			.build();
+
+		var generations = ToolExecutionResult.buildGenerations(toolExecutionResult);
+
+		assertThat(generations).hasSize(1);
+		assertThat(generations.get(0).getOutput().getText()).isNull();
+	}
+
+	@Test
+	void whenToolResponseWithEmptyStringContentThenGenerationWithEmptyText() {
+		var toolExecutionResult = ToolExecutionResult.builder()
+			.conversationHistory(
+					List.of(new ToolResponseMessage(List.of(new ToolResponseMessage.ToolResponse("1", "tool", "")))))
+			.build();
+
+		var generations = ToolExecutionResult.buildGenerations(toolExecutionResult);
+
+		assertThat(generations).hasSize(1);
+		assertThat(generations.get(0).getOutput().getText()).isEmpty();
+		assertThat((String) generations.get(0).getMetadata().get(ToolExecutionResult.METADATA_TOOL_NAME))
+			.isEqualTo("tool");
+	}
+
+	@Test
+	void whenBuilderCalledWithoutConversationHistoryThenThrowsException() {
+		var toolExecutionResult = ToolExecutionResult.builder().build();
+
+		assertThatThrownBy(() -> ToolExecutionResult.buildGenerations(toolExecutionResult))
+			.isInstanceOf(ArrayIndexOutOfBoundsException.class);
+
+		assertThat(toolExecutionResult.conversationHistory()).isNotNull();
+		assertThat(toolExecutionResult.conversationHistory()).isEmpty();
+	}
+
 }