diff --git a/src/cpu.h b/src/cpu.h
index 78be97e..44d6079 100644
--- a/src/cpu.h
+++ b/src/cpu.h
@@ -15,6 +15,9 @@
 #include "ruc/format/formatter.h"
 
 class CPU final : public ProcessingUnit {
+private:
+	friend struct CPUTest;
+
 public:
 	explicit CPU(uint32_t frequency);
 	virtual ~CPU();
diff --git a/test/testcpu.cpp b/test/testcpu.cpp
new file mode 100644
index 0000000..e72d613
--- /dev/null
+++ b/test/testcpu.cpp
@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2022 Riyyi
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "cpu.h"
+#include "macro.h"
+#include "testcase.h"
+#include "testsuite.h"
+
+struct CPUTest {
+	CPU cpu { 0 };
+
+	bool isCarry(uint32_t lhs, uint32_t rhs, uint32_t limit_bit) { return cpu.isCarry(lhs, rhs, limit_bit); }
+};
+
+// -----------------------------------------
+
+TEST_CASE(CPUIsCarry)
+{
+	CPUTest test;
+
+	// 8-bit Half-carry false
+
+	EXPECT_EQ(test.isCarry(56, 17, 0x10), false);
+
+	EXPECT_EQ(test.isCarry(16, -1, 0x10), false);
+	EXPECT_EQ(test.isCarry(32, -1, 0x10), false);
+	EXPECT_EQ(test.isCarry(144, -1, 0x10), false);
+	EXPECT_EQ(test.isCarry(211, -20, 0x10), false);
+
+	// 8-bit Half-carry true
+
+	EXPECT_EQ(test.isCarry(46, 34, 0x10), true);
+	EXPECT_EQ(test.isCarry(62, 34, 0x10), true);
+
+	EXPECT_EQ(test.isCarry(136, -1, 0x10), true);
+	EXPECT_EQ(test.isCarry(219, -20, 0x10), true);
+	EXPECT_EQ(test.isCarry(250, -20, 0x10), true);
+
+	// 8-bit Full carry false
+
+	EXPECT_EQ(test.isCarry(254, 1, 0x100), false);
+
+	// 8-bit Full carry true
+
+	EXPECT_EQ(test.isCarry(254, 2, 0x100), true);
+}
diff --git a/test/testthing.cpp b/test/testthing.cpp
deleted file mode 100644
index 3e71310..0000000
--- a/test/testthing.cpp
+++ /dev/null
@@ -1,17 +0,0 @@
-/*
- * Copyright (C) 2022 Riyyi
- *
- * SPDX-License-Identifier: MIT
- */
-
-#include "macro.h"
-#include "testcase.h"
-#include "testsuite.h"
-
-// -----------------------------------------
-
-TEST_CASE(Thing)
-{
-	int a = 5;
-	EXPECT_EQ(a, 5);
-}