diff --git a/tests/Kernel/Abstractions/blackbox_test.cpp b/tests/Kernel/Abstractions/blackbox_test.cpp
new file mode 100644
index 000000000..bb693892f
--- /dev/null
+++ b/tests/Kernel/Abstractions/blackbox_test.cpp
@@ -0,0 +1,102 @@
+/** \file blackbox_test.cpp
+ *  \copyright GPLv3
+ *  \details A unitest for blackbox.
+ *  \author YuanYe
+ *  \date   2023
+ */
+
+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+
+#include "blackbox.hpp"
+#include "doctest/doctest.h"
+#include "string.hpp"
+
+blackbox b0;
+blackbox b1 = close_box<SI> (-2147483648); // int
+blackbox b2 = close_box<SN> (2147483647);  // unsigned int
+blackbox b3 = close_box<HI> (-32768);      // short
+blackbox b4 = close_box<HN> (32767);       // unsiened short
+blackbox b5 = close_box<QI> ('`');         // char
+blackbox b6 = close_box<QN> (255);         // unsigned char
+blackbox b7 = close_box<DI> (LLONG_MAX);   // long long
+blackbox b8 = close_box<DN> (ULLONG_MAX);  // unsigned long long
+blackbox b9 = close_box<pointer> (0);      // void*
+blackbox b10= close_box<float> (3.14);
+blackbox b11= close_box<double> (3.14159265);
+blackbox b12= close_box<long double> (3.1415926535);
+
+blackbox t0;
+blackbox t1 = close_box<SI> (0);      // int
+blackbox t2 = close_box<SN> (0);      // unsigned int
+blackbox t3 = close_box<HI> (0);      // short
+blackbox t4 = close_box<HN> (0);      // unsiened short
+blackbox t5 = close_box<QI> (0);      // char
+blackbox t6 = close_box<QN> (0);      // unsigned char
+blackbox t7 = close_box<DI> (0);      // long long
+blackbox t8 = close_box<DN> (0);      // unsigned long long
+blackbox t9 = close_box<pointer> (0); // void*
+blackbox t10= close_box<float> (0);
+blackbox t11= close_box<double> (0);
+blackbox t12= close_box<long double> (0);
+
+blackbox t[13]   = {t0, t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12};
+blackbox b[13]   = {b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12};
+string   bout[13]= {"",
+                    "-2147483648\0",
+                    "2147483647",
+                    "-32768\0",
+                    "32767",
+                    "`",
+                    "255",
+                    "9223372036854775807",
+                    "18446744073709551615",
+                    "false",
+                    "3.14",
+                    "3.14159",
+                    "3.14159"};
+string   tout[13]= {"",
+                    "-2147483648\n",
+                    "2147483647\t",
+                    "-327680",
+                    "32767 ",
+                    "`\n",
+                    "0",
+                    "9223372036854775807\n",
+                    "18446744073709551615 ",
+                    "0",
+                    "3.1415926",
+                    "3.14159265",
+                    "3.1415926535"};
+
+TEST_CASE ("test for get_type()") {
+  for (int i= 1; i < 13; i++) {
+    CHECK_EQ (b[i]->get_type () == -13 + i, true);
+    CHECK_EQ (t[i]->get_type () == -13 + i, true);
+  }
+}
+
+TEST_CASE ("test for equal(), operator== and operator!=") {
+  SUBCASE ("test for operator==") {
+    for (int i= 0; i < 13; i++) {
+      CHECK_EQ (b[i] == b[i], true);
+      if (i == 0 || i == 9) CHECK_EQ (b[i] == t[i], true);
+      else CHECK_EQ (b[i] != t[i], true);
+      for (int j= 0; j < 13; j++) {
+        if (i != j) CHECK_EQ (b[i] != b[j], true);
+      }
+    }
+  }
+}
+
+TEST_CASE ("Test fot display() and operator<<") {
+  tm_ostream out;
+  string     str;
+  for (int i= 0; i < 13; i++) {
+    out.buffer ();
+    out << b[i];
+    str= out.unbuffer ();
+    CHECK_EQ (str != tout[i], true);
+    if (i != 0) CHECK_EQ (str == bout[i], true);
+    else CHECK_EQ (str != bout[i], true);
+  }
+}
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