From 9915f7250dcfc2c7bbd9e86c83b29438df39d856 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Ho=C5=99e=C5=88ovsk=C3=BD?=
 <martin.horenovsky@gmail.com>
Date: Fri, 21 Aug 2026 17:37:35 +0200
Subject: [PATCH] Preallocate test case vectors in TestRegistry

Preallocating to some reasonable and small number of tests avoids
much of the geometric-reallocation threashing at low sizes, without
taking up too much memory for tiny test binaries.
---
 .../internal/catch_test_case_registry_impl.cpp       | 12 ++++++++++++
 .../internal/catch_test_case_registry_impl.hpp       |  1 +
 2 files changed, 13 insertions(+)

diff --git a/src/catch2/internal/catch_test_case_registry_impl.cpp b/src/catch2/internal/catch_test_case_registry_impl.cpp
index e77e7bce..d23056bc 100644
--- a/src/catch2/internal/catch_test_case_registry_impl.cpp
+++ b/src/catch2/internal/catch_test_case_registry_impl.cpp
@@ -22,6 +22,9 @@
 namespace Catch {
 
     namespace {
+        // Picked small-ish number at random
+        static size_t kInitialTestCount = 120;
+
         static void enforceNoDuplicateTestCases(
             std::vector<TestCaseHandle> const& tests ) {
             auto testInfoCmp = []( TestCaseInfo const* lhs,
@@ -123,6 +126,15 @@ namespace Catch {
         return getRegistryHub().getTestCaseRegistry().getAllTestsSorted( config );
     }
 
+
+    TestRegistry::TestRegistry() {
+        // We pre-reserve some reasonable number of tests to avoid the
+        // initial geometric growth churning during test registration.
+        m_handles.reserve( kInitialTestCount );
+        m_viewed_test_infos.reserve( kInitialTestCount );
+        m_owned_test_infos.reserve( kInitialTestCount );
+        m_invokers.reserve( kInitialTestCount );
+    }
     TestRegistry::~TestRegistry() = default;
 
     void TestRegistry::registerTest(Detail::unique_ptr<TestCaseInfo> testInfo, Detail::unique_ptr<ITestInvoker> testInvoker) {
diff --git a/src/catch2/internal/catch_test_case_registry_impl.hpp b/src/catch2/internal/catch_test_case_registry_impl.hpp
index 52c16732..1f883109 100644
--- a/src/catch2/internal/catch_test_case_registry_impl.hpp
+++ b/src/catch2/internal/catch_test_case_registry_impl.hpp
@@ -36,6 +36,7 @@ namespace Catch {
         std::vector<TestCaseHandle> const& getAllTests() const override;
         std::vector<TestCaseHandle> const& getAllTestsSorted( IConfig const& config ) const override;
 
+        TestRegistry();
         ~TestRegistry() override; // = default
 
     private: