diff --git a/src/core_test/cases/all_cases.cc b/src/core_test/cases/all_cases.cc
index 1725532..36c3cb3 100644
--- a/src/core_test/cases/all_cases.cc
+++ b/src/core_test/cases/all_cases.cc
@@ -2,6 +2,7 @@
 
 #include "helper/hash.h"
 #include "helper/cases.h"
+#include "helper/fixture.h"
 #include "utility/exposer.h"
 
 #include "short_code/short_code.h"
@@ -28,7 +29,7 @@ constexpr auto ALL_CASES_XXH3 = std::to_array<uint64_t>({
     0x2cdf6c14a7ce3e9a, 0xb9dd04a315583f5c, 0x19046e49c44ae90d, 0x2d06800538d394c2,
 });
 
-class AllCasesTest : public testing::Test, public Concurrent {
+class AllCasesTest : public testing::Test, public helper::Concurrent {
 protected:
     void SetUp() override {
         Reset();
diff --git a/src/core_test/cases/basic_ranges.cc b/src/core_test/cases/basic_ranges.cc
index d76c825..3028175 100644
--- a/src/core_test/cases/basic_ranges.cc
+++ b/src/core_test/cases/basic_ranges.cc
@@ -3,6 +3,7 @@
 #include "group/group.h"
 #include "helper/hash.h"
 #include "helper/cases.h"
+#include "helper/fixture.h"
 #include "utility/exposer.h"
 
 using klotski::array_sum;
@@ -18,7 +19,7 @@ EXPOSE_VAR(BasicRanges, bool, available_)
 
 constexpr uint64_t BASIC_RANGES_XXH3 = 0x34fce9da6a052533;
 
-class BasicRangesTest : public testing::Test, public Concurrent {
+class BasicRangesTest : public testing::Test, public helper::Concurrent {
 protected:
     void SetUp() override {
         Reset();
diff --git a/src/core_test/cases/helper/cases.h b/src/core_test/cases/helper/cases.h
index f60d530..de79fda 100644
--- a/src/core_test/cases/helper/cases.h
+++ b/src/core_test/cases/helper/cases.h
@@ -29,30 +29,6 @@ constexpr auto Heads = std::to_array({
 
 // ----------------------------------------------------------------------------------------- //
 
-/// Test fixture wrapper with concurrency tools.
-class Concurrent {
-protected:
-    // Execute same task concurrently.
-    helper::Racer racer_ {};
-
-    // Execute assigned tasks one by one.
-    helper::Executor serial_ {1};
-
-    // Execute assigned tasks on all cores.
-    helper::Executor executor_ {0};
-
-    // Atomic helpers for multi-thread testing.
-    std::atomic<int> counter_ {0};
-    std::atomic_flag condition_ {false};
-};
-
-/// Test fixture macro with custom test suite name.
-#define TEST_FF(test_suite_name, test_name)                        \
-    GTEST_TEST_(test_suite_name, test_name, test_suite_name##Test, \
-                ::testing::internal::GetTypeId<test_suite_name##Test>())
-
-// ----------------------------------------------------------------------------------------- //
-
 /// Assert that Ranges are sorted and unique.
 #define EXPECT_SORTED_AND_UNIQUE(R)                          \
     EXPECT_TRUE(std::ranges::is_sorted(R.begin(), R.end())); \
diff --git a/src/core_test/helper/fixture.h b/src/core_test/helper/fixture.h
new file mode 100644
index 0000000..fee5525
--- /dev/null
+++ b/src/core_test/helper/fixture.h
@@ -0,0 +1,32 @@
+#pragma once
+
+#include <atomic>
+#include <gtest/gtest.h>
+
+#include "helper/concurrent.h"
+
+namespace helper {
+
+/// Test fixture wrapper with concurrency tools.
+class Concurrent {
+protected:
+    // Execute same task concurrently.
+    Racer racer_ {};
+
+    // Execute assigned tasks one by one.
+    Executor serial_ {1};
+
+    // Execute assigned tasks on all cores.
+    Executor executor_ {0};
+
+    // Atomic helpers for multi-thread testing.
+    std::atomic<int> counter_ {0};
+    std::atomic_flag condition_ {false};
+};
+
+/// Test fixture macro with custom test suite name.
+#define TEST_FF(test_suite_name, test_name)                        \
+    GTEST_TEST_(test_suite_name, test_name, test_suite_name##Test, \
+                ::testing::internal::GetTypeId<test_suite_name##Test>())
+
+} // namespace helper