tests - Add test for memory register

tests/test_memory_register.cpp

@@ -0,0 +1,25 @@
+#include "doctest.h"
+
+#include <cpu/cpu.h>
+#include <memory/bus.h>
+#include <memory/ram.h>
+#include <memory/register.h>
+
+TEST_CASE("IE controllable via bus")
+{
+  u8 test_ram[] = {
+    0x3E, 0xFF, // LD A, $0xFF
+    0xE0, 0xFF, // LDH [FF:FF], A
+  };
+
+  Bus b;
+  Cpu cpu(&b);
+
+  b.map_device(0x0000, 0x0004, new RAM(test_ram, 0x4, true));
+  b.map_device(0xFFFF, 0xFFFF, new BoundRegister(cpu.state.IE));
+
+  cpu.step();
+  cpu.step();
+
+  CHECK(cpu.state.IE == 0xFF);
+}