Initial arena benchmarks

tests/test_arena_allocator.cpp

@@ -90,8 +90,10 @@ TEST_CASE("ArenaAllocator block management") {
     CHECK(ptr1 != ptr2);
   }
 
-  SUBCASE("allocation larger than block size throws") {
-    CHECK_THROWS_AS(arena.allocate(200), std::bad_alloc);
+  SUBCASE("allocation larger than block size grows arena") {
+    void *ptr = arena.allocate(200);
+    CHECK(ptr != nullptr);
+    CHECK(arena.num_blocks() == 2);
   }
 }
 
@@ -160,7 +162,7 @@ TEST_CASE("ArenaAllocator memory tracking") {
 
   arena.allocate(50);
   CHECK(arena.num_blocks() == 2);
-  CHECK(arena.total_allocated() == 1024);
+  CHECK(arena.total_allocated() >= 1024);
 }
 
 TEST_CASE("ArenaAllocator stress test") {
@@ -256,6 +258,39 @@ TEST_CASE("ArenaAllocator with custom objects") {
   CHECK(obj2->name == "second");
 }
 
+TEST_CASE("ArenaAllocator geometric growth policy") {
+  ArenaAllocator arena(64);
+
+  SUBCASE("normal geometric growth doubles size") {
+    arena.allocate(60); // Fill first block
+    size_t initial_total = arena.total_allocated();
+
+    arena.allocate(10); // Force new block
+    CHECK(arena.num_blocks() == 2);
+    CHECK(arena.total_allocated() == initial_total + 128); // 64 * 2 = 128
+  }
+
+  SUBCASE("large allocation creates appropriately sized block") {
+    arena.allocate(60); // Fill first block
+    size_t initial_total = arena.total_allocated();
+
+    arena.allocate(200); // Force large block
+    CHECK(arena.num_blocks() == 2);
+    CHECK(arena.total_allocated() >= initial_total + 200); // At least 200 bytes
+  }
+
+  SUBCASE("multiple growths maintain O(log n) blocks") {
+    size_t allocation_size = 32;
+
+    for (int i = 0; i < 10; ++i) {
+      arena.allocate(allocation_size);
+    }
+
+    // Should have grown logarithmically, not linearly
+    CHECK(arena.num_blocks() < 6); // Much less than 10
+  }
+}
+
 TEST_CASE("ArenaAllocator alignment edge cases") {
   ArenaAllocator arena;