For instance,

• expression_and_test.cpp
• expression_compare_test.cpp
• expression_convert_test.cpp
• expression_date_test.cpp
• expression_field_path_test.cpp
• expression_find_internal_test.cpp
• expression_javascript_test.cpp
• expression_nary_test.cpp
• expression_object_test.cpp
• expression_or_test.cpp
• expression_replace_test.cpp
• expression_test.cpp
• expression_trigonometric_test.cpp
• expression_trim_test.cpp

as well as

• expression_bm.cpp

Use the benchmark test to assess that there is no drop in performance