Catch2 Sections as Macros

Question

I like from the C++ unit test framework Catch2 its sections -- much more than the xUnit test fixtures. Therefore I wrote me some macros which mimic the Catch2 sections.

This is the first macro heavy code I wrote, so I am mostly interested whether the macros do what they should do, or not.

#include <utility>

#define TOKENPASTE_HELPER(x, y) x ## y
#define TOKENPASTE(x, y) TOKENPASTE_HELPER(x, y)

#define CASE( name )                                            \
    if ( int executed_section = 0, first_run = 0; true )        \
    while ( std::exchange(executed_section, 0) || first_run++ == 0 )

#define SECTION( name )                                         \
    static int TOKENPASTE(counter_done_, __LINE__) = 0;         \
        goto TOKENPASTE(section_start_, __LINE__);              \
    TOKENPASTE(section_end_, __LINE__):                         \
        continue;                                               \
    TOKENPASTE(section_start_, __LINE__):                       \
    while ( true )                                              \
        if ( TOKENPASTE(counter_done_, __LINE__) == 2 ) {       \
            break;                                              \
        } else if( TOKENPASTE(counter_done_, __LINE__) == 1 ) { \
            TOKENPASTE(counter_done_, __LINE__) = 2;            \
            goto TOKENPASTE(section_end_, __LINE__);            \
        } else if ( TOKENPASTE(counter_done_, __LINE__) = 1, executed_section=1; true )

They are used like this:

#include <cassert>

int main() {
    CASE( i_test ) {
        int i = 0;

        SECTION( i==1 ) {
            ++i;
            assert( i == 1 );
        }

        SECTION( i == 0 ) {
            assert( i == 0 );
        }
    }

    CASE( ii_test ) {
        int i = 10;
        SECTION() {
            assert( i==10 );
        }
    }
}

Just... sigh. Don't use macros. But since you are using macros, please show the output of gcc -E or equivalent. — Reinderien
– Reinderien, Commented Aug 5 at 1:01

Reinderien · Accepted Answer · 2025-08-05 01:34:32Z

The output of gcc -E is

int main() {
    if ( int executed_section = 0, first_run = 0; true ) while ( std::exchange(executed_section, 0) || first_run++ == 0 ) {
        int i = 0;

        static int counter_done_27 = 0; goto section_start_27; section_end_27: continue; section_start_27: while ( true ) if ( counter_done_27 == 2 ) { break; } else if( counter_done_27 == 1 ) { counter_done_27 = 2; goto section_end_27; } else if ( counter_done_27 = 1, executed_section=1; true ) {
            ++i;
            assert( i == 1 );
        }

        static int counter_done_32 = 0; goto section_start_32; section_end_32: continue; section_start_32: while ( true ) if ( counter_done_32 == 2 ) { break; } else if( counter_done_32 == 1 ) { counter_done_32 = 2; goto section_end_32; } else if ( counter_done_32 = 1, executed_section=1; true ) {
            assert( i == 0 );
        }
    }

    if ( int executed_section = 0, first_run = 0; true ) while ( std::exchange(executed_section, 0) || first_run++ == 0 ) {
        int i = 10;
        static int counter_done_39 = 0; goto section_start_39; section_end_39: continue; section_start_39: while ( true ) if ( counter_done_39 == 2 ) { break; } else if( counter_done_39 == 1 ) { counter_done_39 = 2; goto section_end_39; } else if ( counter_done_39 = 1, executed_section=1; true ) {
            assert( i==10 );
        }
    }
}

I do recommend that you check output like this for macro-heavy code. And... what does it even do. It feels like it's written to be a puzzle, and test frameworks shouldn't be a puzzle. The goto, exchange, non-re-entrant statics... None of this should see the light of day, and it should all be deleted. I strongly recommend that you retry this project and pretend that the precompiler does not exist. The same features can be implemented with contemporary C++, especially lambdas.

While I agree it would be better to write a test framework that doesn't require macros, if the goal is to make a drop-in replacement for Catch2, I don't see how you could do that. — G. Sliepen
– G. Sliepen, Commented Aug 7 at 8:28

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