test: add testbench for num/safe_cast

testbench/yycc/num/safe_cast.cpp

@@ -1,9 +1,51 @@
 #include <gtest/gtest.h>
 #include <yycc.hpp>
 #include <yycc/num/safe_cast.hpp>
+#include <yycc/macro/ptr_size_detector.hpp>
+
+#include <yycc/rust/prelude.hpp>
+
+#define CAST ::yycc::num::safe_cast
 
 namespace yycctest::num::safe_cast {
 
-    // TODO: Add testbench
+    TEST(NumSafeCast, To) {
+        // Definitely okey
+        auto rv = CAST::to<u32, u8>(UINT8_C(1));
+        EXPECT_EQ(rv, UINT32_C(1));
+    }
+
+    TEST(NumSafeCast, TryTo) {
+        // Okey
+        {
+            auto rv = CAST::try_to<u8, u32>(UINT32_C(1));
+            ASSERT_TRUE(rv.has_value());
+            EXPECT_EQ(rv.value(), UINT8_C(1));
+        }
+        // Bad cast
+        {
+            auto rv = CAST::try_to<u8, u32>(UINT32_C(6161));
+            EXPECT_FALSE(rv.has_value());
+        }
+    }
+
+    TEST(NumSafeCast, VariableLength) {
+        // Both 32-bit and 64-bit pointer size are okey.
+        {
+            auto rv = CAST::try_to<usize, u64>(UINT64_C(0x00000000ffffffff));
+            ASSERT_TRUE(rv.has_value());
+            EXPECT_EQ(rv.value(), 0xffffffffu);
+        }
+        // Only 64-bit pointer size is okey.
+        {
+            auto rv = CAST::try_to<usize, u64>(UINT64_C(0xffffffffffffffff));
+#if defined(YYCC_PTRSIZE_64)
+            ASSERT_TRUE(rv.has_value());
+            EXPECT_EQ(rv.value(), 0xffffffffffffffffu);
+#else
+            EXPECT_FALSE(rv.has_value());
+#endif
+        }
+    }
 
 }