Update statement

Hi All, I am passing three date variables in the stored procedure. Depending on whichever variable has value in it, it will be assigned to the Testdate column of the testable. Only one variable will have value others will be nullCreate procedure test( @TestDate datetime =NULL, @Testdate2 dateTime=NULL, @TestDate3 datetime=NULL)ASUpdate testable Set TestDate = @TestDate Its just that depending on whatever variable has value in it that will be assigned to the column TestDate.Any help will be appreciated.