Need help on decision table structure

not enough information yet.

Does every rule consist of the same 5 tests?  if so, all 5 should be distinct columns in a single table.
You might want to consider this structure even if some rules might be missing a couple and simply null them.
(rule_id, test1, test2,test3,test4,test5)


Could each rule have a varying number of tests, possibly even more than 5, and the which types of tests can vary as well?
If so test types should be a separate table and each rule should have one or more rows that join to the test table.

(test_id,  test_description)
(rule_id, test_id, test_result)

I have a table with columns test1 to test5 and more columns.
rule could be based on any one of these columns.

Also in the rule table, there should be a column to store operator(">","<" ...)

I am just confused like how to handle nested conditions
If there are Parent conditions / child conditions like multiple "OR" and "AND". In this case,  what should be the procedure
for this rule

I'm not sure I understand.

I think you might just want a large text column (like varchar2(4000))  to hold the text of your rule
Then you could simply evalute it with substitution

I'm sorry I didn't explain you clearly. I am creating a front end application in apex for creating rules.
I will be having an option to select the column name (from table. this could be test1 or test2 or any column)
                                          then to choose operator (> < = etc.,)
                                          then to choose value ('pass','fail' ...)
what should be the table design to build rule like below.

(test1 = pass or (test2 = fail and test3 = pass))
or (test4 = fail or test5 = pass)

This I can do, but users may not be able to write condition.

if there is something like dropdown available for rule creation, it will be easy for them.

and If I know in which table structure I can store this rule, I can design a front end for them.