test(cpu): add Blargg hardware test ROM harness

tests/GameBoy.Core.Tests/TestRoms.cs

@@ -0,0 +1,37 @@
+using System;
+using System.IO;
+
+namespace GameBoy.Tests
+{
+    internal static class TestRoms
+    {
+        public static string Path(string name)
+        {
+            string path = System.IO.Path.Combine(AppContext.BaseDirectory, "roms", name);
+            if (!File.Exists(path))
+                throw new FileNotFoundException($"test rom not found: {path}");
+            return path;
+        }
+
+        public static byte[] Load(string name) => File.ReadAllBytes(Path(name));
+
+        public static byte[] BuildProgram(params byte[] program)
+        {
+            var rom = new byte[0x8000];
+            rom[0x0147] = 0x00;
+            rom[0x0148] = 0x00;
+            rom[0x0149] = 0x00;
+            Array.Copy(program, 0, rom, 0x0100, program.Length);
+            return rom;
+        }
+
+        public static byte[] BuildCartridge(byte cartridgeType, byte ramSizeCode, int romBanks = 2)
+        {
+            var rom = new byte[0x4000 * romBanks];
+            rom[0x0147] = cartridgeType;
+            rom[0x0148] = 0x00;
+            rom[0x0149] = ramSizeCode;
+            return rom;
+        }
+    }
+}