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_buffer.cpp

@@ -0,0 +1,89 @@
+#include "fixtures/OpenGLTestFixture.h"
+#include "XCEngine/RHI/OpenGL/OpenGLBuffer.h"
+
+using namespace XCEngine::RHI;
+
+TEST_F(OpenGLTestFixture, Buffer_Initialize_VertexBuffer) {
+    OpenGLBuffer buffer;
+    float vertices[] = { 0.0f, 0.0f, 0.5f, 0.5f };
+
+    bool result = buffer.InitializeVertexBuffer(vertices, sizeof(vertices));
+
+    ASSERT_TRUE(result);
+    EXPECT_NE(buffer.GetID(), 0u);
+    EXPECT_EQ(buffer.GetSize(), sizeof(vertices));
+    EXPECT_EQ(buffer.GetType(), OpenGLBufferType::Vertex);
+
+    buffer.Shutdown();
+}
+
+TEST_F(OpenGLTestFixture, Buffer_Initialize_IndexBuffer) {
+    OpenGLBuffer buffer;
+    unsigned int indices[] = { 0, 1, 2 };
+
+    bool result = buffer.InitializeIndexBuffer(indices, sizeof(indices));
+
+    ASSERT_TRUE(result);
+    EXPECT_NE(buffer.GetID(), 0u);
+    EXPECT_EQ(buffer.GetSize(), sizeof(indices));
+
+    buffer.Shutdown();
+}
+
+TEST_F(OpenGLTestFixture, Buffer_Initialize_UniformBuffer) {
+    OpenGLBuffer buffer;
+    float data[16] = {};
+
+    bool result = buffer.Initialize(OpenGLBufferType::Uniform, sizeof(data), data, true);
+
+    ASSERT_TRUE(result);
+    EXPECT_TRUE(buffer.IsDynamic());
+    EXPECT_EQ(buffer.GetType(), OpenGLBufferType::Uniform);
+
+    buffer.Shutdown();
+}
+
+TEST_F(OpenGLTestFixture, Buffer_Initialize_Dynamic) {
+    OpenGLBuffer buffer;
+
+    bool result = buffer.Initialize(OpenGLBufferType::CopyRead, 256, nullptr, true);
+
+    ASSERT_TRUE(result);
+    EXPECT_TRUE(buffer.IsDynamic());
+    EXPECT_EQ(buffer.GetSize(), 256u);
+
+    buffer.Shutdown();
+}
+
+TEST_F(OpenGLTestFixture, Buffer_Bind_Unbind) {
+    OpenGLBuffer buffer;
+    buffer.InitializeVertexBuffer(nullptr, 16);
+
+    buffer.Bind();
+    GLint boundBuffer = 0;
+    glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &boundBuffer);
+    EXPECT_EQ(boundBuffer, static_cast<GLint>(buffer.GetID()));
+
+    buffer.Unbind();
+    glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &boundBuffer);
+    EXPECT_EQ(boundBuffer, 0);
+
+    buffer.Shutdown();
+}
+
+TEST_F(OpenGLTestFixture, Buffer_Map_Unmap) {
+    OpenGLBuffer buffer;
+    buffer.Initialize(OpenGLBufferType::CopyRead, 256, nullptr, true);
+
+    void* mappedData = buffer.Map();
+    ASSERT_NE(mappedData, nullptr);
+
+    memset(mappedData, 0xAB, 256);
+
+    buffer.Unmap();
+
+    GLenum error = glGetError();
+    EXPECT_EQ(error, GL_NO_ERROR);
+
+    buffer.Shutdown();
+}