Perhaps you should try some spelling variations:
equation systems » radiation systems
function systems » function spaces, fusion system, pension systems
function based » functions based, fixation based, fusion based
based testing » based test, care testing
testing tools » using tools

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (( function based testing tools ) or ( ((function systems) OR (equation systems)) usage tools ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( function based testing tools ) OR ( ((function systems) OR (equation systems)) usage tools )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( function based testing tools ) or ( ((function systems) OR (equation systems)) usage tools ))".
• Adding a wildcard symbol may retrieve word variants: (( function based testing tools ) or ( ((function systems) OR (equation systems)) usage tools ))*.