String Generator Expression gives unexpected result

I have the following CMake code:

add_library(iflib INTERFACE)
target_compile_definitions(iflib INTERFACE
    GEN_EXP=$<IF:$<STREQUAL:"test","test">,"EQUAL","DIFFERENT">
)

Which sets the GEN_EXP definition to "EQUAL", as expected.

However, when I compare with a variable:

add_library(iflib INTERFACE)
set(TEST_VAR "test")
target_compile_definitions(iflib INTERFACE
    GEN_EXP=$<IF:$<STREQUAL:${TEST_VAR},"test">,"EQUAL","DIFFERENT">
)

The GEN_EXP definition becomes "DIFFERENT".

Is it not possible to do this kind of comparison in Generator Expressions?

>Solution :

With the variable evaluated the generator expression looks like this:

target_compile_definitions(iflib INTERFACE
    GEN_EXP=$<IF:$<STREQUAL:test,"test">,"EQUAL","DIFFERENT">
)

depending on whether you want to check for quotes in the variable value or not you either need to add the quotes to the content of the variable

set(TEST_VAR "\"test\"")

or change the generator expression removing the quotes around the value to compare to

target_compile_definitions(iflib INTERFACE
    GEN_EXP=$<IF:$<STREQUAL:${TEST_VAR},test>,"EQUAL","DIFFERENT">
)