diff --git a/components/ai_chat/core/browser/BUILD.gn b/components/ai_chat/core/browser/BUILD.gn
index 20851eb6f4b1..df6def23bd78 100644
--- a/components/ai_chat/core/browser/BUILD.gn
+++ b/components/ai_chat/core/browser/BUILD.gn
@@ -159,6 +159,7 @@ if (!is_ios) {
       "//base/test:test_support",
       "//brave/components/ai_chat/core/browser",
       "//brave/components/ai_chat/core/common",
+      "//brave/components/ai_chat/core/common:test_support",
       "//brave/components/ai_chat/core/common/mojom",
       "//brave/components/api_request_helper",
       "//brave/components/brave_component_updater/browser:test_support",
@@ -200,6 +201,7 @@ source_set("test_support") {
 
   deps = [
     "//brave/components/ai_chat/core/browser",
+    "//brave/components/ai_chat/core/common:test_support",
     "//brave/components/ai_chat/core/common/mojom",
     "//services/network/public/cpp",
     "//testing/gmock",
diff --git a/components/ai_chat/core/browser/conversation_handler_unittest.cc b/components/ai_chat/core/browser/conversation_handler_unittest.cc
index a83103fb14d2..b19a413c7d41 100644
--- a/components/ai_chat/core/browser/conversation_handler_unittest.cc
+++ b/components/ai_chat/core/browser/conversation_handler_unittest.cc
@@ -40,6 +40,7 @@
 #include "brave/components/ai_chat/core/common/features.h"
 #include "brave/components/ai_chat/core/common/mojom/ai_chat.mojom.h"
 #include "brave/components/ai_chat/core/common/pref_names.h"
+#include "brave/components/ai_chat/core/common/test_utils.h"
 #include "components/grit/brave_components_strings.h"
 #include "components/os_crypt/async/browser/os_crypt_async.h"
 #include "components/os_crypt/async/browser/test_utils.h"
@@ -1301,18 +1302,7 @@ TEST_F(ConversationHandlerUnitTest, UploadImage) {
   loop2.Run();
   testing::Mock::VerifyAndClearExpectations(&client);
 
-  const std::vector<std::vector<uint8_t>> test_images = {
-      {0x01, 0x02, 0x03, 0x04, 0x05},
-      {0xde, 0xed, 0xbe, 0xef},
-      {0xff, 0xff, 0xff},
-  };
-  std::vector<mojom::UploadedImagePtr> uploaded_images;
-  uploaded_images.emplace_back(mojom::UploadedImage::New(
-      "filename1", sizeof(test_images[0]), test_images[0]));
-  uploaded_images.emplace_back(mojom::UploadedImage::New(
-      "filename2", sizeof(test_images[1]), test_images[1]));
-  uploaded_images.emplace_back(mojom::UploadedImage::New(
-      "filename3", sizeof(test_images[2]), test_images[2]));
+  auto uploaded_images = CreateSampleUploadedImages(3);
 
   // There are uploaded images.
   // Note that this will need to be put at the end of this test suite
@@ -1321,7 +1311,7 @@ TEST_F(ConversationHandlerUnitTest, UploadImage) {
   EXPECT_CALL(delegate, GetUploadedImagesSize()).WillOnce(testing::Return(3));
   EXPECT_CALL(delegate, GetUploadedImages())
       .Times(1)
-      .WillOnce(testing::Return(std::move(uploaded_images)));
+      .WillOnce(testing::Return(Clone(uploaded_images)));
   EXPECT_CALL(delegate, ClearUploadedImages()).Times(1);
   base::RunLoop loop3;
   EXPECT_CALL(client, OnModelDataChanged)
@@ -1338,15 +1328,11 @@ TEST_F(ConversationHandlerUnitTest, UploadImage) {
   auto& last_entry = conversation_handler_->GetConversationHistory().back();
   EXPECT_TRUE(last_entry->uploaded_images);
   const auto& images = last_entry->uploaded_images.value();
-  EXPECT_EQ(images[0]->filename, "filename1");
-  EXPECT_EQ(images[0]->filesize, static_cast<int64_t>(sizeof(test_images[0])));
-  EXPECT_EQ(images[0]->image_data, test_images[0]);
-  EXPECT_EQ(images[1]->filename, "filename2");
-  EXPECT_EQ(images[1]->filesize, static_cast<int64_t>(sizeof(test_images[1])));
-  EXPECT_EQ(images[1]->image_data, test_images[1]);
-  EXPECT_EQ(images[2]->filename, "filename3");
-  EXPECT_EQ(images[2]->filesize, static_cast<int64_t>(sizeof(test_images[2])));
-  EXPECT_EQ(images[2]->image_data, test_images[2]);
+  for (size_t i = 0; i < images.size(); ++i) {
+    EXPECT_EQ(images[i]->filename, uploaded_images[i]->filename);
+    EXPECT_EQ(images[i]->filesize, uploaded_images[i]->filesize);
+    EXPECT_EQ(images[i]->image_data, uploaded_images[i]->image_data);
+  }
 }
 
 TEST_F(ConversationHandlerUnitTest_NoAssociatedContent,
diff --git a/components/ai_chat/core/browser/engine/engine_consumer.cc b/components/ai_chat/core/browser/engine/engine_consumer.cc
index 657e255d4a4d..b86d1c370cb4 100644
--- a/components/ai_chat/core/browser/engine/engine_consumer.cc
+++ b/components/ai_chat/core/browser/engine/engine_consumer.cc
@@ -7,8 +7,9 @@
 
 #include <optional>
 #include <string>
-#include <string_view>
 
+#include "base/base64.h"
+#include "base/strings/strcat.h"
 #include "brave/components/ai_chat/core/common/mojom/ai_chat.mojom.h"
 
 namespace ai_chat {
@@ -29,6 +30,11 @@ bool EngineConsumer::SupportsDeltaTextResponses() const {
   return false;
 }
 
+std::string EngineConsumer::GetImageDataURL(base::span<uint8_t> image_data) {
+  constexpr char kDataUrlPrefix[] = "data:image/png;base64,";
+  return base::StrCat({kDataUrlPrefix, base::Base64Encode(image_data)});
+}
+
 bool EngineConsumer::CanPerformCompletionRequest(
     const ConversationHistory& conversation_history) const {
   if (conversation_history.empty()) {
diff --git a/components/ai_chat/core/browser/engine/engine_consumer.h b/components/ai_chat/core/browser/engine/engine_consumer.h
index 68c4b0b1bd28..5d73f746a8a0 100644
--- a/components/ai_chat/core/browser/engine/engine_consumer.h
+++ b/components/ai_chat/core/browser/engine/engine_consumer.h
@@ -91,6 +91,8 @@ class EngineConsumer {
     max_associated_content_length_ = max_associated_content_length;
   }
 
+  static std::string GetImageDataURL(base::span<uint8_t> image_data);
+
  protected:
   // Check if we should call GenerationCompletedCallback early based on the
   // conversation history. Ex. empty history, or if the last entry is not a
diff --git a/components/ai_chat/core/browser/engine/engine_consumer_claude.h b/components/ai_chat/core/browser/engine/engine_consumer_claude.h
index 96485d86a042..761dbd26745f 100644
--- a/components/ai_chat/core/browser/engine/engine_consumer_claude.h
+++ b/components/ai_chat/core/browser/engine/engine_consumer_claude.h
@@ -9,7 +9,6 @@
 #include <memory>
 #include <string>
 #include <utility>
-#include <vector>
 
 #include "base/memory/weak_ptr.h"
 #include "brave/components/ai_chat/core/browser/ai_chat_credential_manager.h"
diff --git a/components/ai_chat/core/browser/engine/engine_consumer_conversation_api.cc b/components/ai_chat/core/browser/engine/engine_consumer_conversation_api.cc
index 3f5b6299ef9c..132215c4282d 100644
--- a/components/ai_chat/core/browser/engine/engine_consumer_conversation_api.cc
+++ b/components/ai_chat/core/browser/engine/engine_consumer_conversation_api.cc
@@ -11,7 +11,6 @@
 #include <type_traits>
 #include <vector>
 
-#include "base/base64.h"
 #include "base/check.h"
 #include "base/functional/bind.h"
 #include "base/functional/callback.h"
@@ -20,7 +19,6 @@
 #include "base/memory/weak_ptr.h"
 #include "base/numerics/clamped_math.h"
 #include "base/strings/string_split.h"
-#include "base/strings/string_util.h"
 #include "base/time/time.h"
 #include "base/types/expected.h"
 #include "brave/components/ai_chat/core/common/mojom/ai_chat.mojom.h"
@@ -121,17 +119,15 @@ void EngineConsumerConversationAPI::GenerateAssistantResponse(
   const auto& last_entry = conversation_history.back();
   if (last_entry->uploaded_images) {
     size_t counter = 0;
-    constexpr char kImageUrl[] = R"(data:image/png;base64,$1)";
     for (const auto& uploaded_image : last_entry->uploaded_images.value()) {
       // Only send the first uploaded_image becasue llama-vision seems to take
       // the last one if there are multiple images
       if (counter++ > 0) {
         break;
       }
-      const std::string image_url = base::ReplaceStringPlaceholders(
-          kImageUrl, {base::Base64Encode(uploaded_image->image_data)}, nullptr);
       conversation.push_back({mojom::CharacterType::HUMAN,
-                              ConversationEventType::UploadImage, image_url});
+                              ConversationEventType::UploadImage,
+                              GetImageDataURL(uploaded_image->image_data)});
     }
   }
   // history
diff --git a/components/ai_chat/core/browser/engine/engine_consumer_conversation_api_unittest.cc b/components/ai_chat/core/browser/engine/engine_consumer_conversation_api_unittest.cc
index da9a72cd7b2e..e022e9bed0cd 100644
--- a/components/ai_chat/core/browser/engine/engine_consumer_conversation_api_unittest.cc
+++ b/components/ai_chat/core/browser/engine/engine_consumer_conversation_api_unittest.cc
@@ -11,6 +11,7 @@
 #include <type_traits>
 #include <vector>
 
+#include "base/base64.h"
 #include "base/functional/callback.h"
 #include "base/functional/callback_helpers.h"
 #include "base/json/json_writer.h"
@@ -19,6 +20,7 @@
 #include "base/run_loop.h"
 #include "base/test/bind.h"
 #include "base/test/task_environment.h"
+#include "base/test/test_future.h"
 #include "base/test/values_test_util.h"
 #include "base/time/time.h"
 #include "base/types/expected.h"
@@ -26,6 +28,7 @@
 #include "brave/components/ai_chat/core/browser/engine/conversation_api_client.h"
 #include "brave/components/ai_chat/core/browser/engine/engine_consumer.h"
 #include "brave/components/ai_chat/core/common/mojom/ai_chat.mojom.h"
+#include "brave/components/ai_chat/core/common/test_utils.h"
 #include "services/network/public/cpp/shared_url_loader_factory.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -435,11 +438,7 @@ TEST_F(EngineConsumerConversationAPIUnitTest, GenerateEvents_SummarizePage) {
 }
 
 TEST_F(EngineConsumerConversationAPIUnitTest, GenerateEvents_UploadImage) {
-  const std::vector<std::vector<uint8_t>> test_images = {
-      {0x01, 0x02, 0x03, 0x04, 0x05},
-      {0xde, 0xed, 0xbe, 0xef},
-      {0xff, 0xff, 0xff},
-  };
+  auto uploaded_images = CreateSampleUploadedImages(3);
   constexpr char kTestPrompt[] = "Tell the user what is in the image?";
   constexpr char kAssistantResponse[] = "It's a lion!";
   auto* mock_api_client = GetMockConversationAPIClient();
@@ -452,7 +451,10 @@ TEST_F(EngineConsumerConversationAPIUnitTest, GenerateEvents_UploadImage) {
         // Only support one image for now.
         ASSERT_EQ(conversation.size(), 2u);
         EXPECT_EQ(conversation[0].role, mojom::CharacterType::HUMAN);
-        EXPECT_EQ(conversation[0].content, "data:image/png;base64,AQIDBAU=");
+        EXPECT_EQ(
+            conversation[0].content,
+            base::StrCat({"data:image/png;base64,",
+                          base::Base64Encode(uploaded_images[0]->image_data)}));
         EXPECT_EQ(conversation[0].type, ConversationAPIClient::UploadImage);
         EXPECT_EQ(conversation[1].role, mojom::CharacterType::HUMAN);
         EXPECT_EQ(conversation[1].content, kTestPrompt);
@@ -460,28 +462,17 @@ TEST_F(EngineConsumerConversationAPIUnitTest, GenerateEvents_UploadImage) {
         std::move(callback).Run(kAssistantResponse);
       });
 
-  std::vector<mojom::UploadedImagePtr> uploaded_images;
-  uploaded_images.emplace_back(
-      mojom::UploadedImage::New("filename1", 1, test_images[0]));
-  uploaded_images.emplace_back(
-      mojom::UploadedImage::New("filename", 2, test_images[1]));
-  uploaded_images.emplace_back(
-      mojom::UploadedImage::New("filename", 3, test_images[2]));
-
   std::vector<mojom::ConversationTurnPtr> history;
   history.push_back(mojom::ConversationTurn::New(
       std::nullopt, mojom::CharacterType::HUMAN, mojom::ActionType::UNSPECIFIED,
       "What is this image?", kTestPrompt, std::nullopt, std::nullopt,
-      base::Time::Now(), std::nullopt, std::move(uploaded_images), false));
+      base::Time::Now(), std::nullopt, CloneUpdatedImages(uploaded_images),
+      false));
 
-  engine_->GenerateAssistantResponse(
-      false, "", history, "", base::DoNothing(),
-      base::BindLambdaForTesting([&run_loop, kAssistantResponse](
-                                     EngineConsumer::GenerationResult result) {
-        EXPECT_STREQ(result.value().c_str(), kAssistantResponse);
-        run_loop.Quit();
-      }));
-  run_loop.Run();
+  base::test::TestFuture<EngineConsumer::GenerationResult> future;
+  engine_->GenerateAssistantResponse(false, "", history, "", base::DoNothing(),
+                                     future.GetCallback());
+  EXPECT_STREQ(future.Take()->c_str(), kAssistantResponse);
   testing::Mock::VerifyAndClearExpectations(mock_api_client);
 }
 
diff --git a/components/ai_chat/core/browser/engine/engine_consumer_llama.h b/components/ai_chat/core/browser/engine/engine_consumer_llama.h
index 5c2d8e946bec..61d732aeabe6 100644
--- a/components/ai_chat/core/browser/engine/engine_consumer_llama.h
+++ b/components/ai_chat/core/browser/engine/engine_consumer_llama.h
@@ -9,7 +9,6 @@
 #include <memory>
 #include <string>
 #include <utility>
-#include <vector>
 
 #include "base/memory/weak_ptr.h"
 #include "brave/components/ai_chat/core/browser/ai_chat_credential_manager.h"
diff --git a/components/ai_chat/core/browser/engine/engine_consumer_oai.cc b/components/ai_chat/core/browser/engine/engine_consumer_oai.cc
index 86bdc2eb1de0..ee09a7ce3ac6 100644
--- a/components/ai_chat/core/browser/engine/engine_consumer_oai.cc
+++ b/components/ai_chat/core/browser/engine/engine_consumer_oai.cc
@@ -11,7 +11,6 @@
 #include <type_traits>
 #include <vector>
 
-#include "base/base64.h"
 #include "base/functional/bind.h"
 #include "base/functional/callback.h"
 #include "base/functional/callback_helpers.h"
@@ -101,7 +100,6 @@ base::Value::List BuildMessages(
     user_message.Set("text", "These images are uploaded by the users");
     content.Append(std::move(user_message));
     size_t counter = 0;
-    constexpr char kImageUrl[] = R"(data:image/png;base64,$1)";
     // Only send the first uploaded_image becasue llama-vision seems to take the
     // last one if there are multiple uploaded_images
     for (const auto& uploaded_image : last_entry->uploaded_images.value()) {
@@ -110,10 +108,9 @@ base::Value::List BuildMessages(
       }
       base::Value::Dict image;
       image.Set("type", "image_url");
-      const std::string image_url = base::ReplaceStringPlaceholders(
-          kImageUrl, {base::Base64Encode(uploaded_image->image_data)}, nullptr);
       base::Value::Dict image_url_dict;
-      image_url_dict.Set("url", image_url);
+      image_url_dict.Set(
+          "url", EngineConsumer::GetImageDataURL(uploaded_image->image_data));
       image.Set("image_url", std::move(image_url_dict));
       content.Append(std::move(image));
     }
diff --git a/components/ai_chat/core/browser/engine/engine_consumer_oai.h b/components/ai_chat/core/browser/engine/engine_consumer_oai.h
index 7a998a952acd..94d2283b504a 100644
--- a/components/ai_chat/core/browser/engine/engine_consumer_oai.h
+++ b/components/ai_chat/core/browser/engine/engine_consumer_oai.h
@@ -9,7 +9,6 @@
 #include <memory>
 #include <string>
 #include <utility>
-#include <vector>
 
 #include "base/memory/weak_ptr.h"
 #include "brave/components/ai_chat/core/browser/ai_chat_credential_manager.h"
diff --git a/components/ai_chat/core/browser/engine/engine_consumer_oai_unittest.cc b/components/ai_chat/core/browser/engine/engine_consumer_oai_unittest.cc
index 439e77a04d5d..e228495367a3 100644
--- a/components/ai_chat/core/browser/engine/engine_consumer_oai_unittest.cc
+++ b/components/ai_chat/core/browser/engine/engine_consumer_oai_unittest.cc
@@ -11,6 +11,7 @@
 #include <type_traits>
 #include <vector>
 
+#include "base/base64.h"
 #include "base/containers/checked_iterators.h"
 #include "base/functional/callback.h"
 #include "base/functional/callback_helpers.h"
@@ -22,12 +23,14 @@
 #include "base/strings/utf_string_conversions.h"
 #include "base/test/bind.h"
 #include "base/test/task_environment.h"
+#include "base/test/test_future.h"
 #include "base/test/values_test_util.h"
 #include "base/time/time.h"
 #include "base/values.h"
 #include "brave/components/ai_chat/core/browser/engine/engine_consumer.h"
 #include "brave/components/ai_chat/core/browser/engine/test_utils.h"
 #include "brave/components/ai_chat/core/common/mojom/ai_chat.mojom-forward.h"
+#include "brave/components/ai_chat/core/common/test_utils.h"
 #include "components/grit/brave_components_strings.h"
 #include "services/network/public/cpp/shared_url_loader_factory.h"
 #include "testing/gmock/include/gmock/gmock.h"
@@ -446,35 +449,35 @@ TEST_F(EngineConsumerOAIUnitTest, GenerateAssistantResponseEarlyReturn) {
 TEST_F(EngineConsumerOAIUnitTest, GenerateAssistantResponseUploadImage) {
   EngineConsumer::ConversationHistory history;
   auto* client = GetClient();
-  auto run_loop = std::make_unique<base::RunLoop>();
-  const std::vector<std::vector<uint8_t>> test_images = {
-      {0x01, 0x02, 0x03, 0x04, 0x05},
-      {0xde, 0xed, 0xbe, 0xef},
-      {0xff, 0xff, 0xff},
-  };
+  auto uploaded_images = CreateSampleUploadedImages(3);
   constexpr char kTestPrompt[] = "Tell the user what is in the image?";
   constexpr char kAssistantResponse[] = "It's a lion!";
   EXPECT_CALL(*client, PerformRequest(_, _, _, _))
       .WillOnce(
-          [kTestPrompt, kAssistantResponse](
+          [kTestPrompt, kAssistantResponse, &uploaded_images](
               const mojom::CustomModelOptions, base::Value::List messages,
               EngineConsumer::GenerationDataCallback,
               EngineConsumer::GenerationCompletedCallback completed_callback) {
             EXPECT_EQ(*messages[0].GetDict().Find("role"), "system");
 
-            auto expected_dict = ParseJsonDict(R"({
+            constexpr char kJsonTemplate[] = R"({
                  "content": [ {
                     "text": "These images are uploaded by the users",
                     "type": "text"
                  }, {
                     "image_url": {
-                       "url": "data:image/png;base64,AQIDBAU="
+                       "url": "data:image/png;base64,$1"
                     },
                     "type": "image_url"
                  } ],
                  "role": "user"
                 }
-            )");
+            )";
+            const std::string json_str = base::ReplaceStringPlaceholders(
+                kJsonTemplate,
+                {base::Base64Encode(uploaded_images[0]->image_data)}, nullptr);
+            auto expected_dict = ParseJsonDict(json_str);
+
             EXPECT_EQ(messages[1].GetDict(), expected_dict);
 
             EXPECT_EQ(*messages[2].GetDict().Find("role"), "user");
@@ -484,27 +487,15 @@ TEST_F(EngineConsumerOAIUnitTest, GenerateAssistantResponseUploadImage) {
                 .Run(EngineConsumer::GenerationResult(kAssistantResponse));
           });
 
-  std::vector<mojom::UploadedImagePtr> uploaded_images;
-  uploaded_images.emplace_back(
-      mojom::UploadedImage::New("filename1", 1, test_images[0]));
-  uploaded_images.emplace_back(
-      mojom::UploadedImage::New("filename", 2, test_images[1]));
-  uploaded_images.emplace_back(
-      mojom::UploadedImage::New("filename", 3, test_images[2]));
-
   history.push_back(mojom::ConversationTurn::New(
       std::nullopt, mojom::CharacterType::HUMAN, mojom::ActionType::UNSPECIFIED,
       "What is this image?", kTestPrompt, std::nullopt, std::nullopt,
-      base::Time::Now(), std::nullopt, std::move(uploaded_images), false));
-
-  engine_->GenerateAssistantResponse(
-      false, "", history, "", base::DoNothing(),
-      base::BindLambdaForTesting([&run_loop, kAssistantResponse](
-                                     EngineConsumer::GenerationResult result) {
-        EXPECT_STREQ(result.value().c_str(), kAssistantResponse);
-        run_loop->Quit();
-      }));
-  run_loop->Run();
+      base::Time::Now(), std::nullopt, CloneUpdatedImages(uploaded_images),
+      false));
+  base::test::TestFuture<EngineConsumer::GenerationResult> future;
+  engine_->GenerateAssistantResponse(false, "", history, "", base::DoNothing(),
+                                     future.GetCallback());
+  EXPECT_STREQ(future.Take()->c_str(), kAssistantResponse);
   testing::Mock::VerifyAndClearExpectations(client);
 }
 
diff --git a/components/ai_chat/core/browser/test_utils.cc b/components/ai_chat/core/browser/test_utils.cc
index f753925df162..815f9a8c8e54 100644
--- a/components/ai_chat/core/browser/test_utils.cc
+++ b/components/ai_chat/core/browser/test_utils.cc
@@ -8,14 +8,13 @@
 #include <string>
 #include <utility>
 
-#include "base/rand_util.h"
 #include "base/strings/strcat.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/time/time.h"
 #include "base/uuid.h"
 #include "brave/components/ai_chat/core/common/mojom/ai_chat.mojom-forward.h"
 #include "brave/components/ai_chat/core/common/mojom/ai_chat.mojom.h"
-#include "crypto/random.h"
+#include "brave/components/ai_chat/core/common/test_utils.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace ai_chat {
@@ -221,15 +220,9 @@ std::vector<mojom::ConversationTurnPtr> CreateSampleChatHistory(
   for (size_t i = 0; i < num_query_pairs; i++) {
     // query
     std::optional<std::vector<mojom::UploadedImagePtr>> uploaded_images;
-    for (size_t j = 0; j < num_uploaded_images_per_query; ++j) {
-      std::vector<uint8_t> image_data(base::RandGenerator(64));
-      crypto::RandBytes(image_data);
-      if (!uploaded_images) {
-        uploaded_images = std::vector<mojom::UploadedImagePtr>();
-      }
-      uploaded_images->emplace_back(mojom::UploadedImage::New(
-          "filename" + base::NumberToString(base::RandUint64()),
-          sizeof(image_data), image_data));
+    if (num_uploaded_images_per_query) {
+      uploaded_images =
+          CreateSampleUploadedImages(num_uploaded_images_per_query);
     }
     history.push_back(mojom::ConversationTurn::New(
         base::Uuid::GenerateRandomV4().AsLowercaseString(),
diff --git a/components/ai_chat/core/common/BUILD.gn b/components/ai_chat/core/common/BUILD.gn
index 25604afdac5d..b7b17e48e7ff 100644
--- a/components/ai_chat/core/common/BUILD.gn
+++ b/components/ai_chat/core/common/BUILD.gn
@@ -25,6 +25,20 @@ component("common") {
   ]
 }
 
+source_set("test_support") {
+  testonly = true
+  sources = [
+    "test_utils.cc",
+    "test_utils.h",
+  ]
+
+  deps = [
+    "//base",
+    "//brave/components/ai_chat/core/common/mojom",
+    "//crypto",
+  ]
+}
+
 if (!is_ios) {
   source_set("unit_tests") {
     testonly = true
diff --git a/components/ai_chat/core/common/DEPS b/components/ai_chat/core/common/DEPS
new file mode 100644
index 000000000000..259013b159fb
--- /dev/null
+++ b/components/ai_chat/core/common/DEPS
@@ -0,0 +1,4 @@
+include_rules = [
+  "+crypto",
+]
+
diff --git a/components/ai_chat/core/common/test_utils.cc b/components/ai_chat/core/common/test_utils.cc
new file mode 100644
index 000000000000..64e6dfe58021
--- /dev/null
+++ b/components/ai_chat/core/common/test_utils.cc
@@ -0,0 +1,33 @@
+/* Copyright (c) 2025 The Brave Authors. All rights reserved.
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#include "brave/components/ai_chat/core/common/test_utils.h"
+
+#include "base/rand_util.h"
+#include "brave/components/ai_chat/core/common/mojom/ai_chat.mojom.h"
+#include "crypto/random.h"
+
+namespace ai_chat {
+
+std::vector<mojom::UploadedImagePtr> CreateSampleUploadedImages(size_t number) {
+  std::vector<mojom::UploadedImagePtr> uploaded_images;
+  for (size_t i = 0; i < number; ++i) {
+    std::vector<uint8_t> image_data(base::RandGenerator(64));
+    crypto::RandBytes(image_data);
+    uploaded_images.emplace_back(mojom::UploadedImage::New(
+        "filename" + base::NumberToString(i), sizeof(image_data), image_data));
+  }
+  return uploaded_images;
+}
+std::vector<mojom::UploadedImagePtr> CloneUpdatedImages(
+    const std::vector<mojom::UploadedImagePtr>& input) {
+  std::vector<mojom::UploadedImagePtr> output;
+  for (const auto& image : input) {
+    output.emplace_back(image.Clone());
+  }
+  return output;
+}
+
+}  // namespace ai_chat
diff --git a/components/ai_chat/core/common/test_utils.h b/components/ai_chat/core/common/test_utils.h
new file mode 100644
index 000000000000..7489e5ebf63a
--- /dev/null
+++ b/components/ai_chat/core/common/test_utils.h
@@ -0,0 +1,22 @@
+/* Copyright (c) 2025 The Brave Authors. All rights reserved.
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#ifndef BRAVE_COMPONENTS_AI_CHAT_CORE_COMMON_TEST_UTILS_H_
+#define BRAVE_COMPONENTS_AI_CHAT_CORE_COMMON_TEST_UTILS_H_
+
+#include <vector>
+
+#include "brave/components/ai_chat/core/common/mojom/ai_chat.mojom-forward.h"
+
+namespace ai_chat {
+
+std::vector<mojom::UploadedImagePtr> CreateSampleUploadedImages(size_t number);
+
+std::vector<mojom::UploadedImagePtr> CloneUpdatedImages(
+    const std::vector<mojom::UploadedImagePtr>& input);
+
+}  // namespace ai_chat
+
+#endif  // BRAVE_COMPONENTS_AI_CHAT_CORE_COMMON_TEST_UTILS_H_