OpenGL: Restructure tests similar to D3D12 layout

- Move old test files to new unit/integration structure
- Add OpenGL Test Fixture
- Update CMakeLists.txt for new layout
- Add OpenGL_Test_Restructuring_Plan.md

tests/RHI/OpenGL/unit/test_fence.cpp

@@ -0,0 +1,61 @@
+#include "fixtures/OpenGLTestFixture.h"
+#include "XCEngine/RHI/OpenGL/OpenGLFence.h"
+
+using namespace XCEngine::RHI;
+
+TEST_F(OpenGLTestFixture, Fence_Initialize_Unsignaled) {
+    OpenGLFence fence;
+
+    bool result = fence.Initialize(false);
+
+    ASSERT_TRUE(result);
+    EXPECT_EQ(fence.GetStatus(), FenceStatus::Unsignaled);
+
+    fence.Shutdown();
+}
+
+TEST_F(OpenGLTestFixture, Fence_Initialize_Signaled) {
+    OpenGLFence fence;
+
+    bool result = fence.Initialize(true);
+
+    ASSERT_TRUE(result);
+
+    fence.Shutdown();
+}
+
+TEST_F(OpenGLTestFixture, Fence_Signal_Wait) {
+    OpenGLFence fence;
+    fence.Initialize(false);
+
+    fence.Signal(1);
+
+    fence.Wait(1);
+
+    EXPECT_TRUE(fence.IsSignaled());
+    EXPECT_EQ(fence.GetCompletedValue(), 1u);
+
+    fence.Shutdown();
+}
+
+TEST_F(OpenGLTestFixture, Fence_IsSignaled_ReturnsState) {
+    OpenGLFence fence;
+    fence.Initialize(false);
+
+    fence.Signal(1);
+    fence.Wait(1);
+
+    EXPECT_TRUE(fence.IsSignaled());
+
+    fence.Shutdown();
+}
+
+TEST_F(OpenGLTestFixture, Fence_GetStatus_ReturnsCorrect) {
+    OpenGLFence fence;
+    fence.Initialize(false);
+
+    FenceStatus status = fence.GetStatus();
+    EXPECT_TRUE(status == FenceStatus::Signaled || status == FenceStatus::Unsignaled);
+
+    fence.Shutdown();
+}