Irule for different URL's to one URL

It is because, as Bhattman states, iRules (the string command in particular) honors the case of the input value.

TesT != tEst

For that reason, a function like [string tolower ] will "normalize" the data before performing evaluations.

[string tolower "TesT"] == "test"

You could also use [string toupper ]

[string toupper "TesT"] == "TEST"

In lieu of normalization, you'd have to evaluate every possible case variation that the user might submit.

$var = "Test?"
$var = "TEst?"
$var = "TESt?"
$var = "TEST?"
$var = "tEST?"
$var = "teST?"
...

This string normalization function will cost you a CPU cycle or two, but it certainly beats the alternative search of every possible user submitted combination.