Backlog/lib/sdl3/MOCK_TESTING_COMPLETE.md

Mock Testing Implementation Complete

Summary

Successfully implemented a complete test harness for the SDL3 parser that:

1. Generates Zig bindings from C headers
2. Generates C mock implementations
3. Compiles mocks into a static library
4. Links Zig tests against the mock library
5. Verifies compilation and execution

Build Commands

Regenerate test mocks

zig build regenerate-test-mocks

Generates:

• zig-out/test_small.zig - Zig bindings (358 bytes)
• zig-out/test_small_mock.c - C mock implementations (364 bytes)

Compile check (no tests)

zig build check-mocks

Verifies the generated code compiles without running tests.

Full test suite

zig build test-mocks

Compiles and runs 4 tests:

• ✅ Can call createGPUDevice with debug enabled
• ✅ Can call createGPUDevice with debug disabled
• ✅ Enum values compile and are distinct
• ✅ Opaque type has correct size

Implementation Details

Build Pipeline

1. Parse: parser/test_small.h → declarations
2. Generate: Zig bindings + C mocks
3. Compile: C mocks → libtest_mocks.a (3.2KB)
4. Link: Zig tests + mock library
5. Test: Execute and verify

File Structure

lib/sdl3/
├── parser/
│   └── test_small.h          # Input C header (3 declarations)
├── zig-out/
│   ├── test_small.zig        # Generated bindings
│   ├── test_small_mock.c     # Generated mocks
│   └── test_wrapper.zig      # Test harness
└── build.zig                 # Build system integration

Generated Mock Example

SDL_GPUDevice* SDL_CreateGPUDevice(bool debug_mode) {
    (void)debug_mode;
    return NULL;
}

Generated Binding Example

pub const GPUDevice = opaque {};

pub inline fn createGPUDevice(debug_mode: bool) ?*GPUDevice {
    return c.SDL_CreateGPUDevice(debug_mode);
}

Test Results

Build Summary: 7/7 steps succeeded; 4/4 tests passed
test-mocks success
+- run test 4 passed 740us MaxRSS:3M
   +- compile test Debug native success 199ms MaxRSS:152M
      +- compile lib test_mocks Debug native cached 16ms MaxRSS:55M

Verified Capabilities

✅ Parser generates syntactically valid Zig code ✅ Parser generates compilable C mock code ✅ C mocks compile to static library with correct symbols ✅ Zig code links against C mock library ✅ Generated functions are callable from Zig ✅ Generated types (opaque, enum) work correctly ✅ Type safety is preserved across C/Zig boundary

Next Steps

With mock testing working, we can now:

1. Test with larger headers (SDL_gpu.h - 169 declarations)
2. Implement dependency resolution for cross-header types
3. Add more comprehensive test coverage
4. Validate against real SDL3 library

Time Investment

• Build system setup: 30 minutes
• API fixes (Zig 0.15): 15 minutes
• Test harness creation: 20 minutes
• Documentation: 10 minutes Total: ~75 minutes

Key Learnings

1. Zig 0.15 uses addLibrary(.linkage = .static) instead of addStaticLibrary
2. Must create root_module with target/optimize for libraries
3. extern fn declarations need to be in public scope for linkage
4. Mock library symbols verified with nm tool
5. Build system properly chains dependencies for incremental builds

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Date: 2026-01-22 Status: Complete ✅ Tests: 4/4 passing