Add test for LtsTimelineClassic LineMap.h

- Add test_linemap.cpp with 3 tests
- Test empty creation, insert/retrieve, contains
- Follow policy naming convention

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

qt6-after/qt6-migrated-benchmark/tests/test_linemap.cpp

@@ -0,0 +1,39 @@
+#include "Lts/Common/LtsTimelineClassic/LineMap.h"
+
+#include <gtest/gtest.h>
+
+namespace LtsTimelineClassic
+{
+
+class LineMapTest : public ::testing::Test
+{
+  protected:
+    void SetUp() override {}
+
+    void TearDown() override {}
+};
+
+TEST(LineMapTest, CreateEmptyLineMap)
+{
+    LineMap lineMap;
+    EXPECT_TRUE(lineMap.isEmpty());
+}
+
+TEST(LineMapTest, InsertAndRetrieveValue)
+{
+    LineMap lineMap;
+    lineMap.insert(1, 1000);
+
+    EXPECT_EQ(lineMap.value(1), 1000);
+}
+
+TEST(LineMapTest, ContainsKeyAfterInsert)
+{
+    LineMap lineMap;
+    lineMap.insert(5, 5000);
+
+    EXPECT_TRUE(lineMap.contains(5));
+    EXPECT_FALSE(lineMap.contains(3));
+}
+
+} // namespace LtsTimelineClassic