preparing update statement based on input parameters dynamically

preparing update statement based on input parameters dynamically

I have to prepare update statement dynamically in stored procedure based
on 4 input variables.
suppose take test,test1,test2 and test3 are input parameters.
then i have to prepare query like ,please help me to build this:
update emp set empid='1' where test =test and test1=test1 and test2=test2
and test3=test3