One way to do this is with PatternCount ( Text ; SearchString )
If ( patterncount (Field A ; "test" ) >= 1 ; "yes" ; "no" )
PatternCount gives you the ability to search a given text field for a specific string. The return is how many times the string appears. So if it is >= 1 then your string appears at least once. So if you are looking for "test" and it appears in Field A, Patterncount will give >=1 and the test field will show "yes" otherwise it will show "no."
Hope this helps
If( PatternCount ( Field A ; "test" ) ; "Yes" )