SQL & PL/SQL :: Executing Function From String Variable

I'm trying to find a simple way of getting around this. I have a PL/SQL procedure which loops through a list of values in a table. These values are the actual names of the functions I want it to run in sequence. The problem is I can get the string value each time but I need to store the return value of each function into a number variable e.g.

BEGIN
open all_tests;
fetch all_tests BULK COLLECT INTO test_tabl;
close all_tests;

for myindex IN 1..test_tabl.count LOOP

time_taken := test_source1 ==> this will work but how do I avoid hardcoding the name of the function to be executed and use the test_name value instead?? time_taken is declared as a number (ie the return value of each function is a number)

test_detail := test_tabl(myindex).test_name; ==> test_detail now contains the string name of the function
dbms_output.put_line('Test detail is ' || test_detail);
end loop;