diff --git a/CMakeLists.txt b/CMakeLists.txt
index c2524c1..f055304 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,6 +18,28 @@ target_include_directories(glad PUBLIC
 find_package(Freetype REQUIRED)
 include_directories(${FREETYPE_INCLUDE_DIRS})
 
+include(FetchContent)
+FetchContent_Declare(
+        Catch2
+        GIT_REPOSITORY https://github.com/catchorg/Catch2.git
+        GIT_TAG        v3.7.1
+)
+FetchContent_MakeAvailable(Catch2)
+
+add_executable(LayoutEngineTests
+        tests/layout/LayoutEngineTest.cpp
+)
+
+target_include_directories(LayoutEngineTests PRIVATE
+        src
+        lib/glm
+)
+
+target_link_libraries(LayoutEngineTests PRIVATE Catch2::Catch2WithMain)
+
+include(CTest)
+include(Catch)
+catch_discover_tests(LayoutEngineTests)
 
 add_executable(Dicewars_Siedler src/main.cpp
         src/engine/core/Window.cpp
diff --git a/src/engine/core/gui/uiComponent/layout/UiPositioner.cpp b/src/engine/core/gui/uiComponent/layout/UiPositioner.cpp
index 548c486..d62aa9c 100644
--- a/src/engine/core/gui/uiComponent/layout/UiPositioner.cpp
+++ b/src/engine/core/gui/uiComponent/layout/UiPositioner.cpp
@@ -18,7 +18,7 @@ void UiPositioner::applyLayout(const ::LayoutEngine::ComputedLayout &layout) {
 void UiPositioner::compute(const Dimensions &parent) {
     LayoutEngine::NodeLayout node = buildNodeLayout();
 
-    LayoutEngine::ComputedLayout result = LayoutEngine::compute(node, parent);
+    LayoutEngine::ComputedLayout result = LayoutEngine::compute(node, parent, Application::getInstance().getWindow().GetWidth(), Application::getInstance().getWindow().GetHeight());
 
     applyLayout(result);
 }
diff --git a/tests/layout/LayoutEngineTest.cpp b/tests/layout/LayoutEngineTest.cpp
new file mode 100644
index 0000000..2fcf22b
--- /dev/null
+++ b/tests/layout/LayoutEngineTest.cpp
@@ -0,0 +1,127 @@
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/matchers/catch_matchers_floating_point.hpp>
+#include "engine/core/gui/uiComponent/layout/LayoutEngine.h"
+
+using namespace LayoutEngine;
+using Catch::Matchers::WithinAbs;
+const float EPS = 0.001f;
+
+static NodeLayout makeNode(float x, float y, float w, float h) {
+    NodeLayout n;
+    n.layoutStyle.width       = { w, SizeUnit::Percent };
+    n.layoutStyle.height      = { h, SizeUnit::Percent };
+    n.layoutStyle.margin.left = { x, SizeUnit::Percent };
+    n.layoutStyle.margin.top  = { y, SizeUnit::Percent };
+    return n;
+}
+
+static Dimensions screen800x600() {
+    return { 0.f, 0.f, 1.0f, 1.0f };
+}
+
+// ── Basisfälle ───────────────────────────────────────────────────────────────
+
+TEST_CASE("SizeUnit::Pixels wird korrekt normalisiert", "[layout][pixels]") {
+    NodeLayout root;
+    root.layoutStyle.width  = { 400.f, SizeUnit::Pixels };
+    root.layoutStyle.height = { 300.f, SizeUnit::Pixels };
+
+    auto result = compute(root, screen800x600(), 800.f, 600.f);
+
+    REQUIRE_THAT(result.self.width,  WithinAbs(0.5f, EPS));  // 400/800
+    REQUIRE_THAT(result.self.height, WithinAbs(0.5f, EPS));  // 300/600
+}
+
+TEST_CASE("Eigene Dimensionen werden korrekt berechnet", "[layout][self]") {
+    NodeLayout root = makeNode(0.1f, 0.2f, 0.5f, 0.4f);
+    auto result = compute(root, screen800x600(), 800.f, 600.f);
+
+    REQUIRE_THAT(result.self.x,      WithinAbs(0.1f, EPS));
+    REQUIRE_THAT(result.self.y,      WithinAbs(0.2f, EPS));
+    REQUIRE_THAT(result.self.width,  WithinAbs(0.5f, EPS));
+    REQUIRE_THAT(result.self.height, WithinAbs(0.4f, EPS));
+}
+
+TEST_CASE("Kein Kind → leere children-Liste", "[layout][children]") {
+    NodeLayout root = makeNode(0.f, 0.f, 0.5f, 0.5f);
+    auto result = compute(root, screen800x600(), 800.f, 600.f);
+    REQUIRE(result.children.empty());
+}
+
+// ── JustifyContent ───────────────────────────────────────────────────────────
+
+TEST_CASE("JustifyContent::Start – Kinder beginnen bei 0", "[layout][justify]") {
+    NodeLayout root = makeNode(0.f, 0.f, 1.0f, 1.0f);
+    root.layoutStyle.flexDirection  = FlexDirection::Row;
+    root.layoutStyle.justifyContent = JustifyContent::Start;
+    root.children.push_back(makeNode(0.f, 0.f, 0.2f, 1.0f));
+    root.children.push_back(makeNode(0.f, 0.f, 0.2f, 1.0f));
+
+    auto result = compute(root, screen800x600(), 800.f, 600.f);
+    REQUIRE_THAT(result.children[0].self.x, WithinAbs(0.0f, EPS));
+    REQUIRE_THAT(result.children[1].self.x, WithinAbs(0.2f, EPS));
+}
+
+TEST_CASE("JustifyContent::Center – Kind horizontal zentriert", "[layout][justify]") {
+    NodeLayout root = makeNode(0.f, 0.f, 1.0f, 1.0f);
+    root.layoutStyle.flexDirection  = FlexDirection::Row;
+    root.layoutStyle.justifyContent = JustifyContent::Center;
+    root.children.push_back(makeNode(0.f, 0.f, 0.4f, 1.0f));
+
+    auto result = compute(root, screen800x600(), 800.f, 600.f);
+    // remaining = 1.0 - 0.4 = 0.6 → offset = 0.3
+    REQUIRE_THAT(result.children[0].self.x, WithinAbs(0.3f, EPS));
+}
+
+TEST_CASE("JustifyContent::SpaceBetween – Gap korrekt verteilt", "[layout][justify]") {
+    NodeLayout root = makeNode(0.f, 0.f, 1.0f, 1.0f);
+    root.layoutStyle.flexDirection  = FlexDirection::Row;
+    root.layoutStyle.justifyContent = JustifyContent::SpaceBetween;
+    root.children.push_back(makeNode(0.f, 0.f, 0.2f, 1.0f));
+    root.children.push_back(makeNode(0.f, 0.f, 0.2f, 1.0f));
+    root.children.push_back(makeNode(0.f, 0.f, 0.2f, 1.0f));
+
+    auto result = compute(root, screen800x600(), 800.f, 600.f);
+    // remaining = 1.0 - 0.6 = 0.4, gap = 0.2
+    REQUIRE_THAT(result.children[0].self.x, WithinAbs(0.0f, EPS));
+    REQUIRE_THAT(result.children[1].self.x, WithinAbs(0.4f, EPS));
+    REQUIRE_THAT(result.children[2].self.x, WithinAbs(0.8f, EPS));
+}
+
+// ── AlignItems ───────────────────────────────────────────────────────────────
+
+TEST_CASE("AlignItems::Center – Kind vertikal zentriert (Row)", "[layout][align]") {
+    NodeLayout root = makeNode(0.f, 0.f, 1.0f, 1.0f);
+    root.layoutStyle.flexDirection = FlexDirection::Row;
+    root.layoutStyle.alignItems    = AlignItems::Center;
+    root.children.push_back(makeNode(0.f, 0.f, 0.5f, 0.4f));
+
+    auto result = compute(root, screen800x600(), 800.f, 600.f);
+    // remaining = 1.0 - 0.4 = 0.6 → y = 0.3
+    REQUIRE_THAT(result.children[0].self.y, WithinAbs(0.3f, EPS));
+}
+
+TEST_CASE("AlignItems::End – Kind am unteren Rand (Row)", "[layout][align]") {
+    NodeLayout root = makeNode(0.f, 0.f, 1.0f, 1.0f);
+    root.layoutStyle.flexDirection = FlexDirection::Row;
+    root.layoutStyle.alignItems    = AlignItems::End;
+    root.children.push_back(makeNode(0.f, 0.f, 0.5f, 0.4f));
+
+    auto result = compute(root, screen800x600(), 800.f, 600.f);
+    // remaining = 1.0 - 0.4 = 0.6 → y = 0.6
+    REQUIRE_THAT(result.children[0].self.y, WithinAbs(0.6f, EPS));
+}
+
+// ── FlexDirection::Column ────────────────────────────────────────────────────
+
+TEST_CASE("Column: Kinder werden vertikal gestapelt", "[layout][column]") {
+    NodeLayout root = makeNode(0.f, 0.f, 1.0f, 1.0f);
+    root.layoutStyle.flexDirection  = FlexDirection::Column;
+    root.layoutStyle.justifyContent = JustifyContent::Start;
+    root.children.push_back(makeNode(0.f, 0.f, 1.0f, 0.3f));
+    root.children.push_back(makeNode(0.f, 0.f, 1.0f, 0.3f));
+
+    auto result = compute(root, screen800x600(), 800.f, 600.f);
+    REQUIRE_THAT(result.children[0].self.y, WithinAbs(0.0f, EPS));
+    REQUIRE_THAT(result.children[1].self.y, WithinAbs(0.3f, EPS));
+}
\ No newline at end of file