Combination of RowBox and SuperscriptBox create a new line "\n"?

Question

Given the following code:

test[p_] := 
 With[{str = If[p > 0, "+", "-", "+"]}, 
  DisplayForm@
   RowBox[{DisplayForm[SuperscriptBox["J", "P"]], "=", 
     ToString[DisplayForm[SuperscriptBox["3/2", str]]]}]]

I expect an output like

$$J^P=3/2^\pm$$

depending on the sign of $p$.

However, I get the following output:

RowBox[List[DisplayForm[SuperscriptBox["J","P"]],"=","   +\n3/2"]]

Why is the output so mangled? Note the "3/2" appearing last and behind whitespaces and specifically a linebreak \n. How can I fix this?

Version 13.1.0.0 Student Edition (64-bit on Ubuntu 22.04)

Answer 1

You have a superfluous "ToString". Without this:

test[p_] := 
 With[{str = If[p > 0, "+", "-", "+"]}, 
  DisplayForm@
   RowBox[{DisplayForm[SuperscriptBox["J", "P"]], "=", 
     DisplayForm[SuperscriptBox["3/2", str]]}]]

test[1]