diff --git a/tests/unittests/test-csearchagent.cpp b/tests/unittests/test-csearchagent.cpp
new file mode 100644
index 0000000000..feb4baf58f
--- /dev/null
+++ b/tests/unittests/test-csearchagent.cpp
@@ -0,0 +1,435 @@
+/*
+	Copyright (C) 2021, Sakura Editor Organization
+
+	This software is provided 'as-is', without any express or implied
+	warranty. In no event will the authors be held liable for any damages
+	arising from the use of this software.
+
+	Permission is granted to anyone to use this software for any purpose,
+	including commercial applications, and to alter it and redistribute it
+	freely, subject to the following restrictions:
+
+		1. The origin of this software must not be misrepresented;
+		   you must not claim that you wrote the original software.
+		   If you use this software in a product, an acknowledgment
+		   in the product documentation would be appreciated but is
+		   not required.
+
+		2. Altered source versions must be plainly marked as such,
+		   and must not be misrepresented as being the original software.
+
+		3. This notice may not be removed or altered from any source
+		   distribution.
+*/
+
+#include <gtest/gtest.h>
+#include "CSaveAgent.h"
+
+#include <array>
+#include <initializer_list>
+#include <string_view>
+#include <utility>
+#include "doc/logic/CDocLineMgr.h"
+
+namespace {
+
+template <typename T> void SetLines(CDocLineMgr& m, int seq, T begin, T end)
+{
+	for (auto it = begin; it != end; ++it) {
+		CDocLine* line = m.AddNewLine();
+		line->SetDocLineString(it->data(), it->length());
+		line->m_sMark.m_cModified = seq;
+	}
+}
+
+void SetLines(CDocLineMgr& m, int seq, std::initializer_list<std::wstring_view> args)
+{
+	SetLines(m, seq, args.begin(), args.end());
+}
+
+struct RawLineData {
+	const wchar_t* line;
+	int seq;
+};
+
+COpeLineData MakeOpeLineData(std::initializer_list<RawLineData> lines)
+{
+	COpeLineData data;
+	for (RawLineData rawLine : lines) {
+		CLineData line;
+		line.cmemLine = rawLine.line;
+		line.nSeq = rawLine.seq;
+		data.push_back(line);
+	}
+	return data;
+}
+
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	行の一部を置き換える。
+ */
+TEST(CSearchAgent, ReplaceData1)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"AAA\n", L"BBB\n", L"CCC\n"});
+
+	COpeLineData insData = MakeOpeLineData({{L"DDD", 2}});
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(0, 1), CLogicPoint(3, 1));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = &insData;
+	arg.nDelSeq = 1;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 3);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"AAA\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(1))->GetPtr(), L"DDD\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(1))->m_sMark.m_cModified.GetSeq(), 2);
+	EXPECT_STREQ(m.GetLine(CLogicInt(2))->GetPtr(), L"CCC\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(2))->m_sMark.m_cModified.GetSeq(), 1);
+
+	EXPECT_EQ(arg.nInsSeq, 1);
+	EXPECT_EQ(arg.pcmemDeleted->size(), 1);
+	EXPECT_STREQ(arg.pcmemDeleted->at(0).cmemLine.GetStringPtr(), L"BBB");
+	EXPECT_EQ(arg.pcmemDeleted->at(0).nSeq, 1);
+	EXPECT_EQ(arg.nDeletedLineNum, 0);
+	EXPECT_EQ(arg.nInsLineNum, 0);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(3, 1));
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	行全体を置き換える。
+ */
+TEST(CSearchAgent, ReplaceData2)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"AAA\n", L"BBB\n", L"CCC\n"});
+
+	COpeLineData insData = MakeOpeLineData({{L"DDD\n", 2}});
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(0, 1), CLogicPoint(4, 1));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = &insData;
+	arg.nDelSeq = 1;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 3);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"AAA\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(1))->GetPtr(), L"DDD\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(1))->m_sMark.m_cModified.GetSeq(), 2);
+	EXPECT_STREQ(m.GetLine(CLogicInt(2))->GetPtr(), L"CCC\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(2))->m_sMark.m_cModified.GetSeq(), 1);
+
+	EXPECT_EQ(arg.nInsSeq, 0);
+	EXPECT_EQ(arg.pcmemDeleted->size(), 1);
+	EXPECT_STREQ(arg.pcmemDeleted->at(0).cmemLine.GetStringPtr(), L"BBB\n");
+	EXPECT_EQ(arg.pcmemDeleted->at(0).nSeq, 1);
+	EXPECT_EQ(arg.nDeletedLineNum, 1);
+	EXPECT_EQ(arg.nInsLineNum, 1);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(0, 2));
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	行末の改行を削除する。
+ */
+TEST(CSearchAgent, ReplaceData3)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"AAA\n", L"BBB\n", L"CCC\n"});
+
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(3, 1), CLogicPoint(4, 1));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = nullptr;
+	arg.nDelSeq = 1;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 2);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"AAA\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(1))->GetPtr(), L"BBBCCC\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(1))->m_sMark.m_cModified.GetSeq(), 1);
+
+	EXPECT_EQ(arg.nInsSeq, 0);
+	EXPECT_EQ(arg.pcmemDeleted->size(), 2);
+	EXPECT_STREQ(arg.pcmemDeleted->at(0).cmemLine.GetStringPtr(), L"\n");
+	EXPECT_EQ(arg.pcmemDeleted->at(0).nSeq, 1);
+	EXPECT_STREQ(arg.pcmemDeleted->at(1).cmemLine.GetStringPtr(), L"");
+	EXPECT_EQ(arg.pcmemDeleted->at(1).nSeq, 1);
+	EXPECT_EQ(arg.nDeletedLineNum, 1);
+	EXPECT_EQ(arg.nInsLineNum, 0);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(3, 1));
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	行末の改行を削除する。削除するデータ長が長いケース。
+ */
+TEST(CSearchAgent, ReplaceData4)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"AAA\n", L"BBB\n", L"CCC\n"});
+
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(1, 1), CLogicPoint(4, 1));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = nullptr;
+	arg.nDelSeq = 1;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 2);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"AAA\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(1))->GetPtr(), L"BCCC\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(1))->m_sMark.m_cModified.GetSeq(), 1);
+
+	EXPECT_EQ(arg.nInsSeq, 0);
+	EXPECT_EQ(arg.pcmemDeleted->size(), 2);
+	EXPECT_STREQ(arg.pcmemDeleted->at(0).cmemLine.GetStringPtr(), L"BB\n");
+	EXPECT_EQ(arg.pcmemDeleted->at(0).nSeq, 1);
+	EXPECT_STREQ(arg.pcmemDeleted->at(1).cmemLine.GetStringPtr(), L"");
+	EXPECT_EQ(arg.pcmemDeleted->at(1).nSeq, 1);
+	EXPECT_EQ(arg.nDeletedLineNum, 1);
+	EXPECT_EQ(arg.nInsLineNum, 0);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(1, 1));
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	行末の改行を削除する。対象行がデータ末尾であるケース。
+ */
+TEST(CSearchAgent, ReplaceData5)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"AAA\n"});
+
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(3, 0), CLogicPoint(4, 0));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = nullptr;
+	arg.nDelSeq = 1;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"AAA");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 1);
+
+	EXPECT_EQ(arg.nInsSeq, 0);
+	EXPECT_EQ(arg.pcmemDeleted->size(), 1);
+	EXPECT_STREQ(arg.pcmemDeleted->at(0).cmemLine.GetStringPtr(), L"\n");
+	EXPECT_EQ(arg.pcmemDeleted->at(0).nSeq, 1);
+	EXPECT_EQ(arg.nDeletedLineNum, 0);
+	EXPECT_EQ(arg.nInsLineNum, 0);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(3, 0));
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	文字を挿入して複数行を連結する。
+ */
+TEST(CSearchAgent, ReplaceData6)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"AAA\n", L"BBB\n", L"CCC\n"});
+
+	COpeLineData insData = MakeOpeLineData({{L" ", 2}});
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(2, 1), CLogicPoint(1, 2));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = &insData;
+	arg.nDelSeq = 1;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 2);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"AAA\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(1))->GetPtr(), L"BB CC\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(1))->m_sMark.m_cModified.GetSeq(), 2);
+
+	EXPECT_EQ(arg.nInsSeq, 1);
+	EXPECT_EQ(arg.pcmemDeleted->size(), 2);
+	EXPECT_STREQ(arg.pcmemDeleted->at(0).cmemLine.GetStringPtr(), L"B\n");
+	EXPECT_EQ(arg.pcmemDeleted->at(0).nSeq, 1);
+	EXPECT_STREQ(arg.pcmemDeleted->at(1).cmemLine.GetStringPtr(), L"C");
+	EXPECT_EQ(arg.pcmemDeleted->at(1).nSeq, 1);
+	EXPECT_EQ(arg.nDeletedLineNum, 1);
+	EXPECT_EQ(arg.nInsLineNum, 0);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(3, 1));
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	既存行の間に行を挿入し、次の行の先頭に文字を挿入する。
+	先頭に文字を挿入した行がデータの末尾であるケース。
+ */
+TEST(CSearchAgent, ReplaceData7)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"AAA\n", L"BBB\n"});
+
+	COpeLineData insData = MakeOpeLineData({{L"CCC\n", 2}, {L"DDD", 3}});
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(0, 1), CLogicPoint(0, 1));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = &insData;
+	arg.nDelSeq = 0;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 3);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"AAA\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(1))->GetPtr(), L"CCC\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(1))->m_sMark.m_cModified.GetSeq(), 2);
+	EXPECT_STREQ(m.GetLine(CLogicInt(2))->GetPtr(), L"DDDBBB\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(2))->m_sMark.m_cModified.GetSeq(), 3);
+
+	EXPECT_EQ(arg.nInsSeq, 1);
+	EXPECT_TRUE(arg.pcmemDeleted->empty());
+	EXPECT_EQ(arg.nDeletedLineNum, 0);
+	EXPECT_EQ(arg.nInsLineNum, 1);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(3, 2));
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	既存行の間に行を挿入し、次の行の先頭に文字を挿入する。
+	先頭に文字を挿入した行がデータの末尾ではないケース。
+ */
+TEST(CSearchAgent, ReplaceData8)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"AAA\n", L"BBB\n", L"CCC\n"});
+
+	COpeLineData insData = MakeOpeLineData({{L"DDD\n", 2}, {L"EEE", 3}});
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(0, 1), CLogicPoint(0, 1));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = &insData;
+	arg.nDelSeq = 0;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 4);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"AAA\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(1))->GetPtr(), L"DDD\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(1))->m_sMark.m_cModified.GetSeq(), 2);
+	EXPECT_STREQ(m.GetLine(CLogicInt(2))->GetPtr(), L"EEEBBB\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(2))->m_sMark.m_cModified.GetSeq(), 3);
+	EXPECT_STREQ(m.GetLine(CLogicInt(3))->GetPtr(), L"CCC\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(3))->m_sMark.m_cModified.GetSeq(), 1);
+
+	EXPECT_EQ(arg.nInsSeq, 1);
+	EXPECT_TRUE(arg.pcmemDeleted->empty());
+	EXPECT_EQ(arg.nDeletedLineNum, 0);
+	EXPECT_EQ(arg.nInsLineNum, 1);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(3, 2));
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	既存行の末尾に新しい行を追加する。
+ */
+TEST(CSearchAgent, ReplaceData9)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"AAA\n", L"BBB\n"});
+
+	COpeLineData insData = MakeOpeLineData({{L"CCC\n", 2}});
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(0, 2), CLogicPoint(0, 2));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = &insData;
+	arg.nDelSeq = 0;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 3);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"AAA\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(1))->GetPtr(), L"BBB\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(1))->m_sMark.m_cModified.GetSeq(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(2))->GetPtr(), L"CCC\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(2))->m_sMark.m_cModified.GetSeq(), 2);
+
+	EXPECT_EQ(arg.nInsSeq, 0);
+	EXPECT_TRUE(arg.pcmemDeleted->empty());
+	EXPECT_EQ(arg.nDeletedLineNum, 0);
+	EXPECT_EQ(arg.nInsLineNum, 1);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(0, 3));
+}
+
+/*!
+	CSearchAgent::ReplaceData のテスト
+
+	置換後の文字列が既存の行バッファの有効長に収まる場合の最適化済みコードパスの検査。
+ */
+TEST(CSearchAgent, ReplaceData10)
+{
+	CDocLineMgr m;
+	SetLines(m, 1, {L"0123456789\n"});
+	m.GetLine(CLogicInt(0))->_GetDocLineData().AllocStringBuffer(15);
+
+	COpeLineData insData = MakeOpeLineData({{L"0123", 2}});
+	COpeLineData delData;
+
+	DocLineReplaceArg arg;
+	arg.sDelRange = CLogicRange(CLogicPoint(9, 0), CLogicPoint(10, 0));
+	arg.pcmemDeleted = &delData;
+	arg.pInsData = &insData;
+	arg.nDelSeq = 0;
+	arg.nInsSeq = -1;
+	CSearchAgent(&m).ReplaceData(&arg, false);
+
+	EXPECT_EQ(m.GetLineCount(), 1);
+	EXPECT_STREQ(m.GetLine(CLogicInt(0))->GetPtr(), L"0123456780123\n");
+	EXPECT_EQ(m.GetLine(CLogicInt(0))->m_sMark.m_cModified.GetSeq(), 2);
+
+	EXPECT_EQ(arg.nInsSeq, 1);
+	EXPECT_EQ(arg.pcmemDeleted->size(), 1);
+	EXPECT_STREQ(arg.pcmemDeleted->at(0).cmemLine.GetStringPtr(), L"9");
+	EXPECT_EQ(arg.pcmemDeleted->at(0).nSeq, 1);
+	EXPECT_EQ(arg.nDeletedLineNum, 0);
+	EXPECT_EQ(arg.nInsLineNum, 0);
+	EXPECT_EQ(arg.ptNewPos, CLogicPoint(13, 0));
+}
diff --git a/tests/unittests/tests1.vcxproj b/tests/unittests/tests1.vcxproj
index ef960a2e78..547d655a06 100644
--- a/tests/unittests/tests1.vcxproj
+++ b/tests/unittests/tests1.vcxproj
@@ -108,6 +108,7 @@
     <ClCompile Include="code-main.cpp" />
     <ClCompile Include="test-cdocline.cpp" />
     <ClCompile Include="test-cdoclinemgr.cpp" />
+    <ClCompile Include="test-csearchagent.cpp" />
     <ClCompile Include="test-printEFunctionCode.cpp" />
     <ClCompile Include="test-cclipboard.cpp" />
     <ClCompile Include="test-ccodebase.cpp" />
diff --git a/tests/unittests/tests1.vcxproj.filters b/tests/unittests/tests1.vcxproj.filters
index 8577262fe3..371c58a62f 100644
--- a/tests/unittests/tests1.vcxproj.filters
+++ b/tests/unittests/tests1.vcxproj.filters
@@ -145,6 +145,9 @@
     <ClCompile Include="test-cdoclinemgr.cpp">
       <Filter>Test Files</Filter>
     </ClCompile>
+    <ClCompile Include="test-csearchagent.cpp">
+      <Filter>Test Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="StartEditorProcessForTest.h">