nes ppu vbl unit test

// Test raw PPU vblank timing when PPU rendering is off.
TEST(ppu_off_vblank)
{
  static const std::vector<uint8_t> program = {};
  auto emu = createTestEmulator(MapperType::NROM, 2, 1, 0, program);
  auto &ppu = emu->ppu();  // alias for brevity

  ppu.bus_read(IORegisters::PPUSTATUS);  // reset latch
  ppu.bus_write(IORegisters::PPUCTRL, 0);
  ppu.bus_write(IORegisters::PPUMASK, 0);

  // Pre-flight check.
  TEST_EQUAL_INT(0, ppu.getFrame());
  TEST_EQUAL_INT(0, ppu.getOddFrame());
  TEST_EQUAL_INT(PreRenderScanline, ppu.getScanline());
  TEST_EQUAL_INT(0, ppu.getCycle());
  TEST_EQUAL_BYTE(0, ppu.getVBlank());
  TEST_EQUAL_INT(PpuState::PreRender, ppu.getState());

  // Process pre-render scanline, plus one tick to start rendering.
  for (int i = 0; i < 341; i++) {
    ppu.tick();
  }
  TEST_EQUAL_INT(0, ppu.getFrame());
  TEST_EQUAL_INT(0, ppu.getOddFrame());
  TEST_EQUAL_INT(FirstRenderScanline, ppu.getScanline());
  TEST_EQUAL_INT(0, ppu.getCycle());
  TEST_EQUAL_BYTE(0, ppu.getVBlank());
  TEST_EQUAL_INT(PpuState::Render, ppu.getState());

  // Get through render scanlines.
  for (int i = 0; i < 341 * 240; i++) {
    ppu.tick();
  }
  TEST_EQUAL_INT(0, ppu.getFrame());
  TEST_EQUAL_INT(0, ppu.getOddFrame());
  TEST_EQUAL_INT(PostRenderScanline, ppu.getScanline());
  TEST_EQUAL_INT(0, ppu.getCycle());
  TEST_EQUAL_BYTE(0, ppu.getVBlank());
  TEST_EQUAL_INT(PpuState::PostRender, ppu.getState());

  // PostRender scanline.
  for (int i = 0; i < 341; i++) {
    ppu.tick();
  }
  TEST_EQUAL_INT(0, ppu.getFrame());
  TEST_EQUAL_INT(0, ppu.getOddFrame());
  TEST_EQUAL_INT(FirstVBlankScanline, ppu.getScanline());
  TEST_EQUAL_INT(0, ppu.getCycle());
  TEST_EQUAL_BYTE(0, ppu.getVBlank());
  TEST_EQUAL_INT(PpuState::VBlank, ppu.getState());

  // Next tick is right before VBLank on.
  ppu.tick();
  TEST_EQUAL_BYTE(0, ppu.getVBlank());

  // Next tick should turn VBlank on.
  ppu.tick();
  TEST_EQUAL_BYTE(1, ppu.getVBlank());

  // Finish vblank period.
  for (int i = 0; i < 339 + 341 * 19; i++) {
    ppu.tick();
  }
  TEST_EQUAL_INT(1, ppu.getFrame());
  TEST_EQUAL_INT(1, ppu.getOddFrame());
  TEST_EQUAL_INT(PreRenderScanline, ppu.getScanline());
  TEST_EQUAL_INT(0, ppu.getCycle());
  TEST_EQUAL_BYTE(1, ppu.getVBlank());
  TEST_EQUAL_INT(PpuState::PreRender, ppu.getState());

  // Cycle #0 of pre-render does not touch vblank, but cycle #1 does.
  ppu.tick();
  TEST_EQUAL_BYTE(1, ppu.getVBlank());

  // Next tick should turn VBlank off.
  ppu.tick();
  TEST_EQUAL_BYTE(0, ppu.getVBlank());
}