So this means that the IF is not applicable in your context.
What commands are before the $$$TestIf(3) and after  ? 
I think of some  WRITE  $$$TestIf(3) .....    
Or you may try to explicitly write the macro-generated code to see any hidden issue
I'm running a bit out of fantas,y what may go on 

Strange.  It should generate   IF (3>0) {QUIT 5} and accept it.
Could you pls simplify the case for testing to 

#define TestIf(%arr) if %arr>0 QUIT 5

Not yet Halloween, but this looks spooky:
For me, all variants work: 
My versions:
InterSystems Studio Client  2024.1.0 Build 262
Server IRIS for Windows (x86-64) 2024.3 (Build 217U)

Now it's clear   instead of   (%arr > 0)  you simply should write (%arr>0)  
The ObjectScript compiler is interpreting the blank after %arr as an argument terminator

(error on compiling within a class) like: 
#define TestIf(%arr)        if (%arr > 0) { QUIT 5 }    ; no final dot.

#define is an element of ObjectScript
so it has to be embedded in a [Class]Method 
and it is only available within that method

It can't be flying free inside a class definition.

If you need your $$$TestIf(...)  in more than 1 method, you can deposit
it in some TestIf.INC  and include it BEFORE the Class statement !!
Then it is visible to ALL methods.

Attention: You can INCLUDE just 1 single  *.INC in a class definition.
If you need more than 1, you have to cascade it with #include  in  the first *.inc

Include TestIf

Class A.PERSON1 Extends %Library.Persistent
{
Parameter GlobalName = "^.........!"  ;;
/// .......
ClassMethod michael(param) as %Integer
{
    $$$TestIf(param)
 .........
    quit $$$OK
}

The AI example is misleading anyhow, as it just does a $O loop without any action to be done 
*.inc is typically kind of text generation code during compilation. 
What is your expectation for using the *.inc ?

%in and %gn are just text replacement parameters:
%gn is used as globalname, %in as first level subscript

If you just see pre you may have a problem with your  &html< ........>  sequence
that translates to write ........,! including all quoting requirements,

while <pre> any text </pre>  is just straight HTML

and  #(variable)# is a CSP instruction to display the actual content of a variable
and avoid any extra spaces

this may help to get the plain %request object:

k ^SPOOL s %io=$I O 2 u 2 ZW %request c 2 u %io

or whatever object you need to trace

YEAH, it's built for visual CSP pages

From Class Docs.:

Somewhere in the CSP page. This is just ~20% of the content

There are geographies in this world where a Decimal-Comma is used instead of a Decimal-Point.
Never met a Decimal-Pipe  😉 

Just received notice:

Provide a single page view of free space in IRIS DBs
has changed status to: Community Opportunity

Status is:  "NEEDS REVIEW" for almost a month!  
I have a feeling.

Not really surprised. The Python version was in as the first anyhow

I understand that using the IRIS Native API is the important feature.
Is this also valid for IRIS Native API for ObjectScript ????.  
No doubt it is EXTERNAL on a different instance,
talking to the same interface as Java, NodeJS, Python, .NET
facing the same limitations  (Functions !)

From Class Docs:
• classmethod ExportAllClassesIndividual(dirname As %String = "", qspec As %String = "", ByRef errorlog As %String, Charset As %String = "", Package As %String = "*", SubDir As %Boolean = 0) as %Status

Export all the classes as individual XML files to a directory.

This method loops through all the classes, exporting each one as an individual XML file named after the classname to the directory dirname. If you specify a Package, then it exports only this package. If SubDir is true,, the method exports sub-packages as subdirectories.

Now the directory is your list of classes and equal sizes of files 
might most likely mean identical content. Or you do a text compare

You are right. $system.OBJ.Export~whatever is oriented to the Namespace

BUT:
There still seems to be no limitation to map a specific database file
to more than 1 namespace. e.g. USER and MERGER (here Read Only)
Then $system.OBJ.Export~whatever takes what it finds in MERGER.
It's quite a dirty approach and only meant for READING the code, therefore, ReadOnly

In any case, it's safer just to copy the (most likely static) DB of interest
and use it in MERGER