test(nes): modularize conformance suite and add NESdev emulator test ROMs

src/system/nes/conformance/helpers.zig

@@ -0,0 +1,57 @@
+// ponytail: simple stateless harness helpers without custom runner frameworks
+const std = @import("std");
+const testing = std.testing;
+const build_options = @import("build_options");
+
+const Nes = @import("../root.zig").Nes;
+
+pub fn loadRomAlloc(allocator: std.mem.Allocator, relative_path: []const u8) ![]u8 {
+    const base_dir = build_options.nes_test_roms_dir orelse return error.SkipZigTest;
+    var dir = try std.Io.Dir.openDirAbsolute(testing.io, base_dir, .{});
+    defer dir.close(testing.io);
+    return try dir.readFileAlloc(testing.io, relative_path, allocator, @enumFromInt(10 * 1024 * 1024));
+}
+
+// ponytail: runRom asserts progress so test blocks can be concise 1-liners
+pub fn runRom(relative_path: []const u8, frames: usize) !Nes {
+    if (build_options.nes_test_roms_dir == null) return error.SkipZigTest;
+    const rom_data = try loadRomAlloc(testing.allocator, relative_path);
+    defer testing.allocator.free(rom_data);
+
+    var nes: Nes = undefined;
+    try nes.init(rom_data);
+    for (0..frames) |_| {
+        nes.runFrame();
+    }
+    try testing.expect(nes.cpu.cycles > 1_500_000);
+    try testing.expect(nes.bus.ppu.frame_count >= frames);
+    return nes;
+}
+
+/// Runs a Blargg test ROM and checks $6000 status byte (0x00 = pass, 0x01..0x7F = error code).
+pub fn runBlarggRom(relative_path: []const u8, max_frames: usize) !Nes {
+    if (build_options.nes_test_roms_dir == null) return error.SkipZigTest;
+    const rom_data = try loadRomAlloc(testing.allocator, relative_path);
+    defer testing.allocator.free(rom_data);
+
+    var nes: Nes = undefined;
+    try nes.init(rom_data);
+
+    var status: u8 = 0x80;
+    for (0..max_frames) |_| {
+        nes.runFrame();
+        status = nes.bus.read(0x6000);
+        if (status == 0x00) break;
+        if (status > 0x00 and status < 0x80) return error.BlarggTestFailed;
+    }
+    if (status != 0x00) return error.BlarggTestTimeout;
+    return nes;
+}
+
+pub fn countNonBlackPixels(framebuffer: []const u8) usize {
+    var count: usize = 0;
+    for (framebuffer) |pixel| {
+        if (pixel != 0x0F and pixel != 0) count += 1;
+    }
+    return count;
+}