RemoveStringFromCSV: add unit test

Tested: only added a unit test and it passed.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: If68e47545f184b9fa22d701e78fb15b2b1b7949f
diff --git a/user_mgr.hpp b/user_mgr.hpp
index 5c1553b..4a82950 100644
--- a/user_mgr.hpp
+++ b/user_mgr.hpp
@@ -64,6 +64,8 @@
 
 std::string getCSVFromVector(std::span<const std::string> vec);
 
+bool removeStringFromCSV(std::string& csvStr, const std::string& delStr);
+
 /** @class UserMgr
  *  @brief Responsible for managing user accounts over the D-Bus interface.
  */