Testing C++ code

LLT

WIP

This item is work in progress. Content might be incomplete or inconsistent.

LLT (low-level testing) in Unreal Engine is an approach to write plain C++ tests (without dependences on the game runtime). Its the closest alternative to the plain unit tests from other languages. LLT uses Catch2 with some additions. Catch2 is a modern C++ testing framework, independent of Unreal Engine or Epic. Epic differentiates (at least they used to differentiate until version 5.3) between explicit and implicit LLT tests:

• explicit LLT tests are placed into a separate UE module with its own Target.cs. Note: there seems to be good support in VS for it but in Rider support is lacking as of 2026. UE explicit test modules are copmiled into an actual .exe program which can be run from command line and supplying arguments to configure test execution. To compile such modules, Epic recommends to use BuildGraph, with Unreal Build Tool and Visual Studio being the other two options. See more info here
• implicit LLT tests are part of another UE module, placed under Tests directory. Epic seems to be abandoning the approach since the implicit tests are not documented after version 5.3. The implicit tests and built with UBT by supplying the -Mode=Test argument. Running is also simply running the .exe, as with the explicit tests. The last mention of implicit tests is Engine version 5.3 here

Automation Test Framework

This framework is different to LLT that it is integrated into the Editor itself. Tests written in this framework are visible and runnable from the editor UI, and there UI features to organize and structure them, and view their results.

Simple automation tests

Simple automation tests can be placed anywhere in the module in a single .cpp file:

IMPLEMENT_SIMPLE_AUTOMATION_TEST(TestClassName, "Category.Subcategory.Subsubcategory", EAutomationTestFlags::EditorContext)

bool TestClassName::RunTest(const FString& Parameters) {
    // ... test code here
    return true;
}

The macro declares a class called TestClassName, with FAutomationTestBase as parent. You write tests by overriding FAutomationTestBase::RunTest and using its reporting methods (AddError for example). Note that the category string will place the test under Category > Subcategory > Subsubcategory in the editor UI. Note that test behavior, expected context and restrictions is configured by EAutomationTestFlags.