Fix size_t warning windows

Signed-off-by: Emerson Knapp <[email protected]>

rosbag2_cpp/test/rosbag2_cpp/test_circular_message_cache.cpp

@@ -29,6 +29,10 @@ using namespace testing;  // NOLINT
 
 namespace
 {
+inline size_t abs_diff(size_t a, size_t b) {
+   return a < b ? b - a : a - b;
+}
+
 std::shared_ptr<rosbag2_storage::SerializedBagMessage> make_test_msg()
 {
   static uint32_t counter = 0;
@@ -61,7 +65,7 @@ class CircularMessageCacheTest : public Test
 
   virtual ~CircularMessageCacheTest() = default;
 
-  const size_t cache_size_ {1 * 500};  // ~0.5 Kb cache
+  const size_t cache_size_ {1 * 500};  // 500B cache
 };
 
 TEST_F(CircularMessageCacheTest, circular_message_cache_overwrites_old) {
@@ -90,10 +94,11 @@ TEST_F(CircularMessageCacheTest, circular_message_cache_overwrites_old) {
     message_data_size += msg->serialized_data->buffer_length;
   }
 
-  int cache_size_diff = cache_size_ - message_data_size;
+  size_t cache_size_diff = cache_size_ - message_data_size;
+  size_t allowed_diff{10};
 
   // Actual stored data size should be roughly the desired cache size
-  EXPECT_THAT(std::abs(cache_size_diff), Lt(10));
+  EXPECT_THAT(cache_size_diff, Lt(allowed_diff));
 }
 
 TEST_F(CircularMessageCacheTest, circular_message_cache_ensure_empty) {