diff --git a/src/converter/immutable_converter_test.cc b/src/converter/immutable_converter_test.cc
index b3a330c91..614ca3bbe 100644
--- a/src/converter/immutable_converter_test.cc
+++ b/src/converter/immutable_converter_test.cc
@@ -456,37 +456,30 @@ bool AutoPartialSuggestionTestHelper(const ConversionRequest &request) {
 }  // namespace
 
 TEST(ImmutableConverterTest, EnableAutoPartialSuggestion) {
-  const commands::Request request;
   ConversionRequest conversion_request;
-  conversion_request.set_request(&request);
   conversion_request.set_create_partial_candidates(true);
 
   EXPECT_TRUE(AutoPartialSuggestionTestHelper(conversion_request));
 }
 
 TEST(ImmutableConverterTest, DisableAutoPartialSuggestion) {
-  const commands::Request request;
   ConversionRequest conversion_request;
-  conversion_request.set_request(&request);
   conversion_request.set_create_partial_candidates(false);
 
   EXPECT_FALSE(AutoPartialSuggestionTestHelper(conversion_request));
 }
 
 TEST(ImmutableConverterTest, AutoPartialSuggestionDefault) {
-  const commands::Request request;
-  ConversionRequest conversion_request;
-  conversion_request.set_request(&request);
-
+  const ConversionRequest conversion_request;
   EXPECT_FALSE(AutoPartialSuggestionTestHelper(conversion_request));
 }
 
 TEST(ImmutableConverterTest, FirstInnerSegment) {
   commands::Request request;
   request_test_util::FillMobileRequest(&request);
-  ConversionRequest conversion_request;
+  ConversionRequest conversion_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
   conversion_request.set_request_type(ConversionRequest::PREDICTION);
-  conversion_request.set_request(&request);
   conversion_request.set_create_partial_candidates(true);
   conversion_request.set_max_conversion_candidates_size(100);
 
@@ -512,9 +505,9 @@ TEST(ImmutableConverterTest, FirstInnerSegmentFiltering) {
   request_test_util::FillMobileRequest(&request);
   request.mutable_decoder_experiment_params()
       ->set_enable_realtime_conversion_candidate_checker(true);
-  ConversionRequest conversion_request;
+  ConversionRequest conversion_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
   conversion_request.set_request_type(ConversionRequest::PREDICTION);
-  conversion_request.set_request(&request);
   conversion_request.set_create_partial_candidates(true);
   conversion_request.set_max_conversion_candidates_size(100);
 
@@ -582,9 +575,9 @@ TEST(ImmutableConverterTest, FirstInnerSegmentFilteringParams) {
   request.mutable_decoder_experiment_params()
       ->set_realtime_conversion_candidate_checker_cost_max_diff(
           4605);  // 500*log(10000);
-  ConversionRequest conversion_request;
+  ConversionRequest conversion_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
   conversion_request.set_request_type(ConversionRequest::PREDICTION);
-  conversion_request.set_request(&request);
   conversion_request.set_create_partial_candidates(true);
   conversion_request.set_max_conversion_candidates_size(100);
 
diff --git a/src/prediction/user_history_predictor_test.cc b/src/prediction/user_history_predictor_test.cc
index 61237d55a..d03e75d50 100644
--- a/src/prediction/user_history_predictor_test.cc
+++ b/src/prediction/user_history_predictor_test.cc
@@ -2144,10 +2144,7 @@ TEST_F(UserHistoryPredictorTest, IsValidSuggestion) {
 
 TEST_F(UserHistoryPredictorTest, IsValidSuggestionForMixedConversion) {
   UserHistoryPredictor::Entry entry;
-
-  commands::Request request;
-  ConversionRequest conversion_request;
-  conversion_request.set_request(&request);
+  const ConversionRequest conversion_request;
 
   entry.set_suggestion_freq(1);
   EXPECT_TRUE(UserHistoryPredictor::IsValidSuggestionForMixedConversion(
diff --git a/src/request/conversion_request.h b/src/request/conversion_request.h
index d0a054b8b..730438900 100644
--- a/src/request/conversion_request.h
+++ b/src/request/conversion_request.h
@@ -191,7 +191,6 @@ class ConversionRequest {
     DCHECK(request_);
     return *request_;
   }
-  void set_request(const commands::Request *request) { request_ = request; }
 
   const commands::Context &context() const {
     DCHECK(context_);
diff --git a/src/rewriter/a11y_description_rewriter_test.cc b/src/rewriter/a11y_description_rewriter_test.cc
index 4ece4cd52..6b7393cf6 100644
--- a/src/rewriter/a11y_description_rewriter_test.cc
+++ b/src/rewriter/a11y_description_rewriter_test.cc
@@ -70,22 +70,23 @@ class A11yDescriptionRewriterTest : public ::testing::Test {
 };
 
 TEST_F(A11yDescriptionRewriterTest, WithoutData) {
-  ConversionRequest a11y_conv_request;
   commands::Request a11y_request;
-
   a11y_request.set_enable_a11y_description(true);
-  a11y_conv_request.set_request(&a11y_request);
+
+  const ConversionRequest a11y_conv_request =
+      ConversionRequestBuilder().SetRequest(a11y_request).Build();
 
   EXPECT_EQ(GetRewriterWithoutData()->capability(a11y_conv_request),
             RewriterInterface::NOT_AVAILABLE);
 }
 
 TEST_F(A11yDescriptionRewriterTest, FeatureDisabled) {
-  ConversionRequest a11y_conv_request, non_a11y_conv_request;
+  ConversionRequest non_a11y_conv_request;
   commands::Request a11y_request;
 
   a11y_request.set_enable_a11y_description(true);
-  a11y_conv_request.set_request(&a11y_request);
+  const ConversionRequest a11y_conv_request =
+      ConversionRequestBuilder().SetRequest(a11y_request).Build();
 
   EXPECT_EQ(GetRewriter()->capability(a11y_conv_request),
             RewriterInterface::ALL);
diff --git a/src/rewriter/date_rewriter_test.cc b/src/rewriter/date_rewriter_test.cc
index 5b2fda2e9..6188cc644 100644
--- a/src/rewriter/date_rewriter_test.cc
+++ b/src/rewriter/date_rewriter_test.cc
@@ -972,18 +972,20 @@ TEST_F(DateRewriterTest, NumberRewriterFromRawInputTest) {
 }
 
 TEST_F(DateRewriterTest, MobileEnvironmentTest) {
-  ConversionRequest convreq;
   commands::Request request;
-  convreq.set_request(&request);
   DateRewriter rewriter;
 
   {
     request.set_mixed_conversion(true);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter.capability(convreq), RewriterInterface::ALL);
   }
 
   {
     request.set_mixed_conversion(false);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter.capability(convreq), RewriterInterface::CONVERSION);
   }
 }
diff --git a/src/rewriter/english_variants_rewriter_test.cc b/src/rewriter/english_variants_rewriter_test.cc
index f38ef67f3..172c1f637 100644
--- a/src/rewriter/english_variants_rewriter_test.cc
+++ b/src/rewriter/english_variants_rewriter_test.cc
@@ -164,11 +164,12 @@ TEST_F(EnglishVariantsRewriterTest, RewriteTest) {
   // 'Google Japan'
   {
     Segments segments;
-    ConversionRequest conversion_request;
     commands::Request request;
     request.mutable_decoder_experiment_params()
         ->set_english_variation_space_insertion_mode(1);
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request = ConversionRequestBuilder()
+            .SetRequest(request)
+            .Build();
 
     Segment *seg1 = segments.push_back_segment();
     Segment *seg2 = segments.push_back_segment();
@@ -216,11 +217,12 @@ TEST_F(EnglishVariantsRewriterTest, RewriteTest) {
   // '<NO CANDIDATE> Japan'
   {
     Segments segments;
-    ConversionRequest conversion_request;
     commands::Request request;
     request.mutable_decoder_experiment_params()
         ->set_english_variation_space_insertion_mode(1);
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request = ConversionRequestBuilder()
+            .SetRequest(request)
+            .Build();
 
     Segment *seg1 = segments.push_back_segment();
     Segment *seg2 = segments.push_back_segment();
@@ -249,11 +251,12 @@ TEST_F(EnglishVariantsRewriterTest, RewriteTest) {
   // 'ぐーぐるJapan'
   {
     Segments segments;
-    ConversionRequest conversion_request;
     commands::Request request;
     request.mutable_decoder_experiment_params()
         ->set_english_variation_space_insertion_mode(1);
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request = ConversionRequestBuilder()
+            .SetRequest(request)
+            .Build();
 
     Segment *seg1 = segments.push_back_segment();
     Segment *seg2 = segments.push_back_segment();
@@ -566,17 +569,20 @@ TEST_F(EnglishVariantsRewriterTest, FillConsumedKeySize) {
 }
 
 TEST_F(EnglishVariantsRewriterTest, MobileEnvironmentTest) {
-  ConversionRequest convreq;
   commands::Request request;
-  convreq.set_request(&request);
 
   {
     request.set_mixed_conversion(true);
+    const ConversionRequest convreq = ConversionRequestBuilder()
+            .SetRequest(request)
+            .Build();
     EXPECT_EQ(rewriter_->capability(convreq), RewriterInterface::ALL);
   }
 
   {
     request.set_mixed_conversion(false);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter_->capability(convreq), RewriterInterface::CONVERSION);
   }
 }
diff --git a/src/rewriter/environmental_filter_rewriter_test.cc b/src/rewriter/environmental_filter_rewriter_test.cc
index 8a6d7d5b6..17f408023 100644
--- a/src/rewriter/environmental_filter_rewriter_test.cc
+++ b/src/rewriter/environmental_filter_rewriter_test.cc
@@ -285,9 +285,9 @@ TEST_F(EnvironmentalFilterRewriterTest, EmojiFilterTest) {
     commands::Request request;
     request.add_additional_renderable_character_groups(
         commands::Request::EMOJI_13_0);
-    ConversionRequest conversion_request;
+    const ConversionRequest conversion_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
     Segments segments;
-    conversion_request.set_request(&request);
 
     segments.Clear();
     AddSegment("a", {"🛻", "🤵‍♀", "🥸"}, &segments);
@@ -315,9 +315,9 @@ TEST_F(EnvironmentalFilterRewriterTest, EmojiFilterE160Test) {
     commands::Request request;
     request.add_additional_renderable_character_groups(
         commands::Request::EMOJI_16_0);
-    ConversionRequest conversion_request;
     Segments segments;
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
 
     segments.Clear();
     AddSegment("えもじ", {"🪏", "🫆", "🫟"}, &segments);
@@ -349,9 +349,7 @@ TEST_F(EnvironmentalFilterRewriterTest, NoRemoveTest) {
 
 TEST_F(EnvironmentalFilterRewriterTest, CandidateFilterTest) {
   {
-    commands::Request request;
-    ConversionRequest conversion_request;
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request;
 
     Segments segments;
     segments.Clear();
@@ -365,9 +363,7 @@ TEST_F(EnvironmentalFilterRewriterTest, CandidateFilterTest) {
   }
 
   {
-    commands::Request request;
-    ConversionRequest conversion_request;
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request;
 
     Segments segments;
     segments.Clear();
@@ -389,8 +385,8 @@ TEST_F(EnvironmentalFilterRewriterTest, CandidateFilterTest) {
     commands::Request request;
     request.add_additional_renderable_character_groups(
         commands::Request::EMPTY);
-    ConversionRequest conversion_request;
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
 
     Segments segments;
     segments.Clear();
@@ -407,8 +403,8 @@ TEST_F(EnvironmentalFilterRewriterTest, CandidateFilterTest) {
     commands::Request request;
     request.add_additional_renderable_character_groups(
         commands::Request::KANA_SUPPLEMENT_6_0);
-    ConversionRequest conversion_request;
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
 
     Segments segments;
     segments.Clear();
@@ -427,8 +423,8 @@ TEST_F(EnvironmentalFilterRewriterTest, CandidateFilterTest) {
         commands::Request::KANA_SUPPLEMENT_6_0);
     request.add_additional_renderable_character_groups(
         commands::Request::KANA_SUPPLEMENT_AND_KANA_EXTENDED_A_10_0);
-    ConversionRequest conversion_request;
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
 
     Segments segments;
     segments.Clear();
@@ -449,8 +445,8 @@ TEST_F(EnvironmentalFilterRewriterTest, CandidateFilterTest) {
         commands::Request::KANA_SUPPLEMENT_AND_KANA_EXTENDED_A_10_0);
     request.add_additional_renderable_character_groups(
         commands::Request::KANA_EXTENDED_A_14_0);
-    ConversionRequest conversion_request;
-    conversion_request.set_request(&request);
+    const ConversionRequest conversion_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
 
     Segments segments;
     segments.Clear();
diff --git a/src/rewriter/merger_rewriter_test.cc b/src/rewriter/merger_rewriter_test.cc
index 456cad3a4..6b17b6ec9 100644
--- a/src/rewriter/merger_rewriter_test.cc
+++ b/src/rewriter/merger_rewriter_test.cc
@@ -171,8 +171,8 @@ TEST_F(MergerRewriterTest, RewriteSuggestionWithMixedConversion) {
   // should result that the merger rewriter does not trim exceeded suggestions.
   commands::Request commands_request;
   commands_request.set_mixed_conversion(true);
-  ConversionRequest request;
-  request.set_request(&commands_request);
+  ConversionRequest request =
+      ConversionRequestBuilder().SetRequest(commands_request).Build();
   request.set_request_type(ConversionRequest::SUGGESTION);
   EXPECT_TRUE(request.request().mixed_conversion());
 
diff --git a/src/rewriter/number_rewriter_test.cc b/src/rewriter/number_rewriter_test.cc
index 51645de6f..4b26624bc 100644
--- a/src/rewriter/number_rewriter_test.cc
+++ b/src/rewriter/number_rewriter_test.cc
@@ -909,18 +909,20 @@ TEST_F(NumberRewriterTest, PreserveUserDictionaryAttribute) {
 TEST_F(NumberRewriterTest, DuplicateCandidateTest) {
   // To reproduce issue b/6714268.
   std::unique_ptr<NumberRewriter> number_rewriter(CreateNumberRewriter());
-  ConversionRequest convreq;
   commands::Request request;
-  convreq.set_request(&request);
   std::unique_ptr<NumberRewriter> rewriter(CreateNumberRewriter());
 
   {
     request.set_mixed_conversion(true);
+    const ConversionRequest convreq =
+      ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter->capability(convreq), RewriterInterface::ALL);
   }
 
   {
     request.set_mixed_conversion(false);
+    const ConversionRequest convreq =
+      ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter->capability(convreq), RewriterInterface::CONVERSION);
   }
 }
diff --git a/src/rewriter/order_rewriter_test.cc b/src/rewriter/order_rewriter_test.cc
index 9ac5f90e7..5edaa11f4 100644
--- a/src/rewriter/order_rewriter_test.cc
+++ b/src/rewriter/order_rewriter_test.cc
@@ -55,9 +55,7 @@ class OrderRewriterTest : public testing::TestWithTempUserProfile {
   }
 
   ConversionRequest CreateConversionRequest(const commands::Request &request) {
-    ConversionRequest convreq;
-    convreq.set_request(&request);
-    return convreq;
+    return ConversionRequestBuilder().SetRequest(request).Build();
   }
 
   std::unique_ptr<OrderRewriter> rewriter_;
diff --git a/src/rewriter/remove_redundant_candidate_rewriter_test.cc b/src/rewriter/remove_redundant_candidate_rewriter_test.cc
index 92ec7f6fb..fd57fda43 100644
--- a/src/rewriter/remove_redundant_candidate_rewriter_test.cc
+++ b/src/rewriter/remove_redundant_candidate_rewriter_test.cc
@@ -66,13 +66,17 @@ TEST(RemoveRedundantCandidateRewriterTest, NoRemoveTest) {
 
 TEST(RemoveRedundantCandidateRewriterTest, CapabilityTest) {
   RemoveRedundantCandidateRewriter rewriter;
-  ConversionRequest convreq;
   commands::Request request;
-  convreq.set_request(&request);
-  { EXPECT_EQ(rewriter.capability(convreq), RewriterInterface::NOT_AVAILABLE); }
+  {
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
+    EXPECT_EQ(rewriter.capability(convreq), RewriterInterface::NOT_AVAILABLE);
+  }
 
   {
     request.set_mixed_conversion(true);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter.capability(convreq), RewriterInterface::ALL);
   }
 }
diff --git a/src/rewriter/single_kanji_rewriter_test.cc b/src/rewriter/single_kanji_rewriter_test.cc
index 87ad60a10..bfc2bb1f6 100644
--- a/src/rewriter/single_kanji_rewriter_test.cc
+++ b/src/rewriter/single_kanji_rewriter_test.cc
@@ -84,6 +84,10 @@ class SingleKanjiRewriterTest : public testing::TestWithTempUserProfile {
     return false;
   }
 
+  static ConversionRequest ConvReq(const commands::Request &request) {
+    return ConversionRequestBuilder().SetRequest(request).Build();
+  }
+
   const ConversionRequest default_request_;
   std::unique_ptr<testing::MockDataManager> data_manager_;
   PosMatcher pos_matcher_;
@@ -92,11 +96,9 @@ class SingleKanjiRewriterTest : public testing::TestWithTempUserProfile {
 TEST_F(SingleKanjiRewriterTest, CapabilityTest) {
   std::unique_ptr<SingleKanjiRewriter> rewriter(CreateSingleKanjiRewriter());
 
-  ConversionRequest convreq;
   commands::Request request;
-  convreq.set_request(&request);
-
   request.set_mixed_conversion(false);
+  const ConversionRequest convreq = ConvReq(request);
   EXPECT_EQ(rewriter->capability(convreq), RewriterInterface::CONVERSION);
 }
 
@@ -123,18 +125,18 @@ TEST_F(SingleKanjiRewriterTest, SetKeyTest) {
 }
 
 TEST_F(SingleKanjiRewriterTest, MobileEnvironmentTest) {
-  ConversionRequest convreq;
   commands::Request request;
-  convreq.set_request(&request);
   std::unique_ptr<SingleKanjiRewriter> rewriter(CreateSingleKanjiRewriter());
 
   {
     request.set_mixed_conversion(true);
+    const ConversionRequest convreq = ConvReq(request);
     EXPECT_EQ(rewriter->capability(convreq), RewriterInterface::ALL);
   }
 
   {
     request.set_mixed_conversion(false);
+    const ConversionRequest convreq = ConvReq(request);
     EXPECT_EQ(rewriter->capability(convreq), RewriterInterface::CONVERSION);
   }
 }
@@ -245,9 +247,8 @@ TEST_F(SingleKanjiRewriterTest, TriggerConditionForPrediction) {
 
     commands::Request request;
     request_test_util::FillMobileRequest(&request);
-    ConversionRequest convreq;
+    ConversionRequest convreq = ConvReq(request);
     convreq.set_request_type(ConversionRequest::PREDICTION);
-    convreq.set_request(&request);
     ASSERT_TRUE(rewriter.capability(convreq) & RewriterInterface::PREDICTION);
     EXPECT_FALSE(rewriter.Rewrite(convreq, &segments));
   }
@@ -258,9 +259,8 @@ TEST_F(SingleKanjiRewriterTest, TriggerConditionForPrediction) {
 
     commands::Request request;
     request_test_util::FillMobileRequestWithHardwareKeyboard(&request);
-    ConversionRequest convreq;
+    ConversionRequest convreq = ConvReq(request);
     convreq.set_request_type(ConversionRequest::PREDICTION);
-    convreq.set_request(&request);
     ASSERT_FALSE(rewriter.capability(convreq) & RewriterInterface::PREDICTION);
   }
 
@@ -270,9 +270,8 @@ TEST_F(SingleKanjiRewriterTest, TriggerConditionForPrediction) {
 
     commands::Request request;
     request_test_util::FillMobileRequestWithHardwareKeyboard(&request);
-    ConversionRequest convreq;
+    ConversionRequest convreq = ConvReq(request);
     convreq.set_request_type(ConversionRequest::CONVERSION);
-    convreq.set_request(&request);
     ASSERT_TRUE(rewriter.capability(convreq) & RewriterInterface::CONVERSION);
     EXPECT_TRUE(rewriter.Rewrite(convreq, &segments));
   }
@@ -284,11 +283,10 @@ TEST_F(SingleKanjiRewriterTest, NoVariationTest) {
   Segments segments;
   InitSegments("かみ", "神", &segments);  // U+795E
 
-  ConversionRequest svs_convreq;
   commands::Request request;
   request.mutable_decoder_experiment_params()->set_variation_character_types(
       commands::DecoderExperimentParams::NO_VARIATION);
-  svs_convreq.set_request(&request);
+  ConversionRequest svs_convreq = ConvReq(request);
 
   EXPECT_EQ(segments.segment(0).candidates_size(), 1);
   EXPECT_TRUE(rewriter.Rewrite(svs_convreq, &segments));
@@ -302,11 +300,10 @@ TEST_F(SingleKanjiRewriterTest, SvsVariationTest) {
   Segments segments;
   InitSegments("かみ", "神", &segments);  // U+795E
 
-  ConversionRequest svs_convreq;
   commands::Request request;
   request.mutable_decoder_experiment_params()->set_variation_character_types(
       commands::DecoderExperimentParams::SVS_JAPANESE);
-  svs_convreq.set_request(&request);
+  ConversionRequest svs_convreq = ConvReq(request);
 
   EXPECT_EQ(segments.segment(0).candidates_size(), 1);
   EXPECT_TRUE(rewriter.Rewrite(svs_convreq, &segments));
diff --git a/src/rewriter/symbol_rewriter_test.cc b/src/rewriter/symbol_rewriter_test.cc
index 8162875bd..d2bc9d0c7 100644
--- a/src/rewriter/symbol_rewriter_test.cc
+++ b/src/rewriter/symbol_rewriter_test.cc
@@ -252,8 +252,8 @@ TEST_F(SymbolRewriterTest, InsertSymbolsPositionMobileSymbolKey) {
   SymbolRewriter symbol_rewriter(converter_, data_manager_.get());
   commands::Request command_request;
   request_test_util::FillMobileRequest(&command_request);
-  ConversionRequest request;
-  request.set_request(&command_request);
+  const ConversionRequest request =
+      ConversionRequestBuilder().SetRequest(command_request).Build();
 
   {
     Segments segments;
@@ -276,8 +276,8 @@ TEST_F(SymbolRewriterTest, InsertSymbolsPositionMobileAlphabetKey) {
   SymbolRewriter symbol_rewriter(converter_, data_manager_.get());
   commands::Request command_request;
   request_test_util::FillMobileRequest(&command_request);
-  ConversionRequest request;
-  request.set_request(&command_request);
+  const ConversionRequest request =
+      ConversionRequestBuilder().SetRequest(command_request).Build();
 
   {
     Segments segments;
@@ -320,18 +320,20 @@ TEST_F(SymbolRewriterTest, SetKey) {
 }
 
 TEST_F(SymbolRewriterTest, MobileEnvironmentTest) {
-  ConversionRequest convreq;
   commands::Request request;
-  convreq.set_request(&request);
   SymbolRewriter rewriter(converter_, data_manager_.get());
 
   {
     request.set_mixed_conversion(true);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter.capability(convreq), RewriterInterface::ALL);
   }
 
   {
     request.set_mixed_conversion(false);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter.capability(convreq), RewriterInterface::CONVERSION);
   }
 }
diff --git a/src/rewriter/t13n_promotion_rewriter_test.cc b/src/rewriter/t13n_promotion_rewriter_test.cc
index 1e65912e9..1a2c1eb97 100644
--- a/src/rewriter/t13n_promotion_rewriter_test.cc
+++ b/src/rewriter/t13n_promotion_rewriter_test.cc
@@ -105,9 +105,7 @@ TEST_F(T13nPromotionRewriterTest, Capability) {
   EXPECT_EQ(rewriter.capability(mobile_conv_request), RewriterInterface::ALL);
 
   // Desktop
-  commands::Request default_request;
   ConversionRequest default_conv_request;
-  default_conv_request.set_request(&default_request);
   EXPECT_EQ(rewriter.capability(default_conv_request),
             RewriterInterface::NOT_AVAILABLE);
 }
diff --git a/src/rewriter/transliteration_rewriter_test.cc b/src/rewriter/transliteration_rewriter_test.cc
index 8ffaa304d..a292c5095 100644
--- a/src/rewriter/transliteration_rewriter_test.cc
+++ b/src/rewriter/transliteration_rewriter_test.cc
@@ -482,18 +482,20 @@ TEST_F(TransliterationRewriterTest, NoRewriteTest) {
 }
 
 TEST_F(TransliterationRewriterTest, MobileEnvironmentTest) {
-  ConversionRequest convreq;
   commands::Request request;
-  convreq.set_request(&request);
   std::unique_ptr<TransliterationRewriter> rewriter(
       CreateTransliterationRewriter());
   {
     request.set_mixed_conversion(true);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter->capability(convreq), RewriterInterface::ALL);
   }
 
   {
     request.set_mixed_conversion(false);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter->capability(convreq), RewriterInterface::CONVERSION);
   }
 }
diff --git a/src/rewriter/user_segment_history_rewriter_test.cc b/src/rewriter/user_segment_history_rewriter_test.cc
index f9a06e9c7..ab23fb1f0 100644
--- a/src/rewriter/user_segment_history_rewriter_test.cc
+++ b/src/rewriter/user_segment_history_rewriter_test.cc
@@ -1391,8 +1391,10 @@ INSTANTIATE_TEST_SUITE_P(
 
 TEST_P(UserSegmentHistoryNumberTest, UserSegmentHistoryRewriterTest) {
   const commands::Request request = GetParam();
-  ConversionRequest convreq = CreateConversionRequest();
-  convreq.set_request(&request);
+  const ConversionRequest convreq = ConversionRequestBuilder()
+                                        .SetConfig(*config_)
+                                        .SetRequest(request)
+                                        .Build();
 
   SetNumberForm(Config::FULL_WIDTH);
   Segments segments;
diff --git a/src/rewriter/variants_rewriter_test.cc b/src/rewriter/variants_rewriter_test.cc
index fc83ffc0b..fa8e49f20 100644
--- a/src/rewriter/variants_rewriter_test.cc
+++ b/src/rewriter/variants_rewriter_test.cc
@@ -704,8 +704,8 @@ TEST_F(VariantsRewriterTest, RewriteForMixedConversion) {
   std::unique_ptr<VariantsRewriter> rewriter(CreateVariantsRewriter());
   Request request;
   request.set_mixed_conversion(true);  // Request mixed conversion.
-  ConversionRequest conv_request;
-  conv_request.set_request(&request);
+  ConversionRequest conv_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
   conv_request.set_request_type(ConversionRequest::SUGGESTION);
   {
     Segments segments;
@@ -785,8 +785,8 @@ TEST_F(VariantsRewriterTest, RewriteForPartialSuggestion) {
   std::unique_ptr<VariantsRewriter> rewriter(CreateVariantsRewriter());
   Request request;
   request.set_mixed_conversion(true);  // Request mixed conversion.
-  ConversionRequest conv_request;
-  conv_request.set_request(&request);
+  ConversionRequest conv_request =
+      ConversionRequestBuilder().SetRequest(request).Build();
   conv_request.set_request_type(ConversionRequest::SUGGESTION);
   {
     Segments segments;
diff --git a/src/rewriter/version_rewriter_test.cc b/src/rewriter/version_rewriter_test.cc
index 56f44888c..c46955ee2 100644
--- a/src/rewriter/version_rewriter_test.cc
+++ b/src/rewriter/version_rewriter_test.cc
@@ -85,18 +85,20 @@ TEST_F(VersionRewriterTest, CapabilityTest) {
 }
 
 TEST_F(VersionRewriterTest, MobileEnvironmentTest) {
-  ConversionRequest convreq;
   commands::Request request;
-  convreq.set_request(&request);
   VersionRewriter rewriter(kDummyDataVersion);
 
   {
     request.set_mixed_conversion(true);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter.capability(convreq), RewriterInterface::ALL);
   }
 
   {
     request.set_mixed_conversion(false);
+    const ConversionRequest convreq =
+        ConversionRequestBuilder().SetRequest(request).Build();
     EXPECT_EQ(rewriter.capability(convreq), RewriterInterface::CONVERSION);
   }
 }