refactor: Example tool and utils: replace Optional<List<T>> with List<T>, add recommended test coverage

core/src/main/java/com/google/adk/tools/ExampleTool.java

@@ -47,7 +47,7 @@
 public final class ExampleTool extends BaseTool {
 
   private final Optional<BaseExampleProvider> exampleProvider;
-  private final Optional<List<Example>> examples;
+  private final List<Example> examples;
 
   /** Single private constructor; create via builder or fromConfig. */
   private ExampleTool(Builder builder) {
@@ -57,7 +57,7 @@ private ExampleTool(Builder builder) {
             ? "Adds few-shot examples to the request"
             : builder.description);
     this.exampleProvider = builder.provider;
-    this.examples = builder.examples.isEmpty() ? Optional.empty() : Optional.of(builder.examples);
+    this.examples = builder.examples;
   }
 
   @Override
@@ -77,9 +77,9 @@ public Completable processLlmRequest(
     final String examplesBlock;
     if (exampleProvider.isPresent()) {
       examplesBlock = ExampleUtils.buildExampleSi(exampleProvider.get(), query);
-    } else if (examples.isPresent()) {
+    } else if (!examples.isEmpty()) {
       // Adapter provider that returns a fixed list irrespective of query
-      BaseExampleProvider provider = q -> examples.get();
+      BaseExampleProvider provider = (unusedQuery) -> examples;
       examplesBlock = ExampleUtils.buildExampleSi(provider, query);
     } else {
       return Completable.complete();
@@ -157,6 +157,7 @@ public static Builder builder() {
     return new Builder();
   }
 
+  /** Builder for {@link ExampleTool}. */
   public static final class Builder {
     private final List<Example> examples = new ArrayList<>();
     private String name = "example_tool";

core/src/test/java/com/google/adk/flows/llmflows/ExamplesTest.java

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.adk.flows.llmflows;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.adk.agents.InvocationContext;
+import com.google.adk.agents.LlmAgent;
+import com.google.adk.agents.RunConfig;
+import com.google.adk.examples.BaseExampleProvider;
+import com.google.adk.examples.Example;
+import com.google.adk.models.LlmRequest;
+import com.google.common.collect.ImmutableList;
+import com.google.genai.types.Content;
+import com.google.genai.types.Part;
+import java.util.List;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public final class ExamplesTest {
+
+  private static class TestExampleProvider implements BaseExampleProvider {
+    @Override
+    public List<Example> getExamples(String query) {
+      return ImmutableList.of(
+          Example.builder()
+              .input(Content.fromParts(Part.fromText("input1")))
+              .output(
+                  ImmutableList.of(
+                      Content.builder().parts(Part.fromText("output1")).role("model").build()))
+              .build());
+    }
+  }
+
+  @Test
+  public void processRequest_withExampleProvider_addsExamplesToInstructions() {
+    LlmAgent agent =
+        LlmAgent.builder().name("test-agent").exampleProvider(new TestExampleProvider()).build();
+    InvocationContext context =
+        InvocationContext.builder()
+            .invocationId("invocation1")
+            .agent(agent)
+            .userContent(Content.fromParts(Part.fromText("what is up?")))
+            .runConfig(RunConfig.builder().build())
+            .build();
+    LlmRequest request = LlmRequest.builder().build();
+    Examples examplesProcessor = new Examples();
+
+    RequestProcessor.RequestProcessingResult result =
+        examplesProcessor.processRequest(context, request).blockingGet();
+
+    assertThat(result.updatedRequest().getSystemInstructions()).isNotEmpty();
+    assertThat(result.updatedRequest().getSystemInstructions().get(0))
+        .contains("[user]\ninput1\n\n[model]\noutput1\n");
+  }
+
+  @Test
+  public void processRequest_withoutExampleProvider_doesNotAddExamplesToInstructions() {
+    LlmAgent agent = LlmAgent.builder().name("test-agent").build();
+    InvocationContext context =
+        InvocationContext.builder()
+            .invocationId("invocation1")
+            .agent(agent)
+            .userContent(Content.fromParts(Part.fromText("what is up?")))
+            .runConfig(RunConfig.builder().build())
+            .build();
+    LlmRequest request = LlmRequest.builder().build();
+    Examples examplesProcessor = new Examples();
+
+    RequestProcessor.RequestProcessingResult result =
+        examplesProcessor.processRequest(context, request).blockingGet();
+
+    assertThat(result.updatedRequest().getSystemInstructions()).isEmpty();
+  }
+}

core/src/test/java/com/google/adk/tools/ExampleToolTest.java

@@ -71,6 +71,43 @@ public void processLlmRequest_withInlineExamples_appendsFewShot() {
     assertThat(si).contains("qout");
   }
 
+  @Test
+  public void processLlmRequest_withProvider_appendsFewShot() {
+    ExampleTool tool = ExampleTool.builder().setExampleProvider(ProviderHolder.EXAMPLES).build();
+
+    InvocationContext ctx = newContext();
+    LlmRequest.Builder builder = LlmRequest.builder().model("gemini-2.0-flash");
+
+    tool.processLlmRequest(builder, ToolContext.builder(ctx).build()).blockingAwait();
+    LlmRequest updated = builder.build();
+
+    assertThat(updated.getSystemInstructions()).isNotEmpty();
+    String si = String.join("\n", updated.getSystemInstructions());
+    assertThat(si).contains("Begin few-shot");
+    assertThat(si).contains("qin");
+    assertThat(si).contains("qout");
+  }
+
+  @Test
+  public void processLlmRequest_withEmptyUserContent_doesNotAppendFewShot() {
+    ExampleTool tool = ExampleTool.builder().addExample(makeExample("qin", "qout")).build();
+    InvocationContext ctxWithContent = newContext();
+    InvocationContext ctx =
+        InvocationContext.builder()
+            .invocationId(ctxWithContent.invocationId())
+            .agent(ctxWithContent.agent())
+            .session(ctxWithContent.session())
+            .userContent(Content.fromParts(Part.fromText("")))
+            .runConfig(ctxWithContent.runConfig())
+            .build();
+    LlmRequest.Builder builder = LlmRequest.builder().model("gemini-2.0-flash");
+
+    tool.processLlmRequest(builder, ToolContext.builder(ctx).build()).blockingAwait();
+    LlmRequest updated = builder.build();
+
+    assertThat(updated.getSystemInstructions()).isEmpty();
+  }
+
   @Test
   public void fromConfig_withInlineExamples_buildsTool() throws Exception {
     BaseTool.ToolArgsConfig args = new BaseTool.ToolArgsConfig();
@@ -95,7 +132,7 @@ public void fromConfig_withInlineExamples_buildsTool() throws Exception {
   /** Holder for a provider referenced via ClassName.FIELD reflection. */
   static final class ProviderHolder {
     public static final BaseExampleProvider EXAMPLES =
-        (query) -> ImmutableList.of(makeExample("qin", "qout"));
+        (unusedQuery) -> ImmutableList.of(makeExample("qin", "qout"));
 
     private ProviderHolder() {}
   }
@@ -255,7 +292,8 @@ public void fromConfig_withWrongTypeProviderField_throwsConfigurationException()
   /** Holder with non-static field for testing. */
   static final class NonStaticProviderHolder {
     @SuppressWarnings("ConstantField") // Intentionally non-static for testing
-    public final BaseExampleProvider INSTANCE = (query) -> ImmutableList.of(makeExample("q", "a"));
+    public final BaseExampleProvider INSTANCE =
+        (unusedQuery) -> ImmutableList.of(makeExample("q", "a"));
 
     private NonStaticProviderHolder() {}
   }