test(nes): consolidate and simplify inline subsystem unit tests

src/system/nes/mapper/nrom.zig

@@ -0,0 +1,83 @@
+const std = @import("std");
+const common = @import("../common.zig");
+const Mirroring = common.Mirroring;
+
+pub const Nrom = @This();
+
+mirroring_mode: Mirroring,
+
+pub fn init(initial_mirroring: Mirroring) Nrom {
+    return .{ .mirroring_mode = initial_mirroring };
+}
+
+pub fn cpuRead(_: *const Nrom, address: u16, prg_rom: []const u8, prg_ram: []const u8) ?u8 {
+    if (address >= 0x6000 and address <= 0x7fff) {
+        const offset = address - 0x6000;
+        if (offset < prg_ram.len) return prg_ram[offset];
+        return 0;
+    }
+    if (address >= 0x8000 and address <= 0xffff) {
+        const mask: usize = if (prg_rom.len <= 0x4000) 0x3fff else 0x7fff;
+        const offset = (address - 0x8000) & mask;
+        if (offset < prg_rom.len) return prg_rom[offset];
+        return 0;
+    }
+    return null;
+}
+
+pub fn cpuWrite(_: *Nrom, address: u16, value: u8, prg_ram: []u8) bool {
+    if (address >= 0x6000 and address <= 0x7fff) {
+        const offset = address - 0x6000;
+        if (offset < prg_ram.len) {
+            prg_ram[offset] = value;
+            return true;
+        }
+    }
+    return false;
+}
+
+pub fn ppuRead(_: *const Nrom, address: u16, chr_rom: []const u8, chr_ram: []const u8, chr_is_ram: bool) ?u8 {
+    if (address < 0x2000) {
+        if (chr_is_ram) {
+            if (address < chr_ram.len) return chr_ram[address];
+        } else {
+            if (chr_rom.len > 0) return chr_rom[address & (chr_rom.len - 1)];
+        }
+        return 0;
+    }
+    return null;
+}
+
+pub fn ppuWrite(_: *Nrom, address: u16, value: u8, chr_ram: []u8, chr_is_ram: bool) bool {
+    if (address < 0x2000 and chr_is_ram) {
+        if (address < chr_ram.len) {
+            chr_ram[address] = value;
+            return true;
+        }
+    }
+    return false;
+}
+
+pub fn mirroring(self: *const Nrom) Mirroring {
+    return self.mirroring_mode;
+}
+
+pub fn irqLine(_: *const Nrom) bool {
+    return false;
+}
+
+pub fn notifyPpuAddress(_: *Nrom, _: u16) void {}
+
+test "nrom prg mirroring" {
+    var nrom = Nrom.init(.horizontal);
+    var prg_16k: [0x4000]u8 = undefined;
+    @memset(&prg_16k, 0x42);
+    prg_16k[0] = 0x11;
+
+    var ram: [0x2000]u8 = undefined;
+    @memset(&ram, 0);
+
+    // 16K PRG is mirrored at $8000 and $C000
+    try std.testing.expectEqual(@as(?u8, 0x11), nrom.cpuRead(0x8000, &prg_16k, &ram));
+    try std.testing.expectEqual(@as(?u8, 0x11), nrom.cpuRead(0xc000, &prg_16k, &ram));
+}