diff --git a/src/core_test/codec/common_code.cc b/src/core_test/codec/common_code.cc
index 68afc8a..c7032b0 100644
--- a/src/core_test/codec/common_code.cc
+++ b/src/core_test/codec/common_code.cc
@@ -36,9 +36,8 @@ TEST(CommonCode, basic) {
     EXPECT_EQ(CommonCode::unsafe_create(TEST_MIRROR_C2).to_horizontal_mirror(), TEST_MIRROR_C2_HM);
 
 #ifndef KLSK_NDEBUG
-    std::ostringstream out;
-    out << CommonCode::unsafe_create(TEST_C_CODE); // ostream capture
-    EXPECT_EQ(out.str(), TEST_C_CODE_STR);
+    EXPECT_OSTREAM(CommonCode::unsafe_create(0), "000000000");
+    EXPECT_OSTREAM(CommonCode::unsafe_create(TEST_C_CODE), TEST_C_CODE_STR);
 #endif
 }
 
diff --git a/src/core_test/codec/helper/codec.h b/src/core_test/codec/helper/codec.h
index 7d8182a..cbd42d2 100644
--- a/src/core_test/codec/helper/codec.h
+++ b/src/core_test/codec/helper/codec.h
@@ -17,6 +17,18 @@ std::vector<uint64_t> all_common_codes();
 
 // ----------------------------------------------------------------------------------------- //
 
+/// Capture ostream output as string.
+template <typename T>
+std::string ostream_capture(T obj) {
+    std::ostringstream out;
+    out << obj; // ostream capture
+    return out.str();
+}
+
+#define EXPECT_OSTREAM(obj, expect) EXPECT_EQ(ostream_capture(obj), expect)
+
+// ----------------------------------------------------------------------------------------- //
+
 /// Spawn all valid RawCodes in parallel.
 void raw_code_parallel(std::function<void(std::span<RawCode>)> &&func);
 
diff --git a/src/core_test/codec/raw_code.cc b/src/core_test/codec/raw_code.cc
index 4518658..554d90e 100644
--- a/src/core_test/codec/raw_code.cc
+++ b/src/core_test/codec/raw_code.cc
@@ -31,9 +31,10 @@ TEST(RawCode, basic) {
     EXPECT_EQ(RawCode::unsafe_create(TEST_MIRROR_R2).to_horizontal_mirror(), TEST_MIRROR_R2_HM);
 
 #ifndef KLSK_NDEBUG
-    std::ostringstream out;
-    out << RawCode::unsafe_create(TEST_R_CODE); // ostream capture
-    EXPECT_EQ(out.str(), "603EDF5CAFFF5E2\n| @ + |\n+ + + +\n| ~ + |\n+ * * +\n* . . *\n");
+    EXPECT_OSTREAM(RawCode::unsafe_create(0x3F03C),
+                   "00000000003F03C\n@ + . .\n+ + . .\n. . . .\n. . . .\n. . . .\n");
+    EXPECT_OSTREAM(RawCode::unsafe_create(TEST_R_CODE),
+                   "603EDF5CAFFF5E2\n| @ + |\n+ + + +\n| ~ + |\n+ * * +\n* . . *\n");
 #endif
 }
 
diff --git a/src/core_test/codec/short_code.cc b/src/core_test/codec/short_code.cc
index c587ea9..8577034 100644
--- a/src/core_test/codec/short_code.cc
+++ b/src/core_test/codec/short_code.cc
@@ -52,9 +52,8 @@ TEST(ShortCode, basic) {
     EXPECT_EQ(sum, SHORT_CODE_LIMIT);
 
 #ifndef KLSK_NDEBUG
-    std::ostringstream out;
-    out << ShortCode::unsafe_create(TEST_S_CODE); // ostream capture
-    EXPECT_EQ(out.str(), TEST_S_CODE_STR);
+    EXPECT_OSTREAM(ShortCode::unsafe_create(0), "11111");
+    EXPECT_OSTREAM(ShortCode::unsafe_create(TEST_S_CODE), TEST_S_CODE_STR);
 #endif
 }