feat: add RHI abstraction layer unit tests

- Add RHITestFixture with RHI_BACKEND env var support for backend selection
- Add unit tests for: Device, Buffer, Texture, SwapChain, CommandList, CommandQueue, Shader, Fence, Sampler
- Tests can run against D3D12 or OpenGL backends via RHI_BACKEND env var
- Add integration folder placeholder for future integration tests

tests/RHI/unit/test_buffer.cpp

@@ -0,0 +1,134 @@
+#include "fixtures/RHITestFixture.h"
+#include "XCEngine/RHI/RHIBuffer.h"
+
+using namespace XCEngine::RHI;
+
+TEST_F(RHITestFixture, Buffer_Map_Unmap) {
+    BufferDesc desc = {};
+    desc.size = 256;
+    desc.stride = sizeof(float);
+    desc.bufferType = static_cast<uint32_t>(BufferType::Vertex);
+
+    RHIBuffer* buffer = GetDevice()->CreateBuffer(desc);
+    ASSERT_NE(buffer, nullptr);
+
+    void* data = buffer->Map();
+    ASSERT_NE(data, nullptr);
+
+    memset(data, 0xAB, 256);
+    buffer->Unmap();
+
+    buffer->Shutdown();
+    delete buffer;
+}
+
+TEST_F(RHITestFixture, Buffer_SetData) {
+    BufferDesc desc = {};
+    desc.size = 128;
+    desc.stride = sizeof(float);
+    desc.bufferType = static_cast<uint32_t>(BufferType::Vertex);
+
+    RHIBuffer* buffer = GetDevice()->CreateBuffer(desc);
+    ASSERT_NE(buffer, nullptr);
+
+    float testData[16] = {};
+    buffer->SetData(testData, sizeof(testData));
+
+    buffer->Shutdown();
+    delete buffer;
+}
+
+TEST_F(RHITestFixture, Buffer_GetSize) {
+    BufferDesc desc = {};
+    desc.size = 1024;
+    desc.stride = sizeof(float);
+    desc.bufferType = static_cast<uint32_t>(BufferType::Vertex);
+
+    RHIBuffer* buffer = GetDevice()->CreateBuffer(desc);
+    ASSERT_NE(buffer, nullptr);
+
+    EXPECT_EQ(buffer->GetSize(), 1024u);
+
+    buffer->Shutdown();
+    delete buffer;
+}
+
+TEST_F(RHITestFixture, Buffer_GetStride) {
+    BufferDesc desc = {};
+    desc.size = 256;
+    desc.stride = 16;
+    desc.bufferType = static_cast<uint32_t>(BufferType::Vertex);
+
+    RHIBuffer* buffer = GetDevice()->CreateBuffer(desc);
+    ASSERT_NE(buffer, nullptr);
+
+    EXPECT_EQ(buffer->GetStride(), 16u);
+
+    buffer->Shutdown();
+    delete buffer;
+}
+
+TEST_F(RHITestFixture, Buffer_SetBufferType) {
+    BufferDesc desc = {};
+    desc.size = 256;
+    desc.stride = sizeof(float);
+    desc.bufferType = static_cast<uint32_t>(BufferType::Vertex);
+
+    RHIBuffer* buffer = GetDevice()->CreateBuffer(desc);
+    ASSERT_NE(buffer, nullptr);
+
+    EXPECT_EQ(buffer->GetBufferType(), BufferType::Vertex);
+    buffer->SetBufferType(BufferType::Index);
+    EXPECT_EQ(buffer->GetBufferType(), BufferType::Index);
+
+    buffer->Shutdown();
+    delete buffer;
+}
+
+TEST_F(RHITestFixture, Buffer_StateManagement) {
+    BufferDesc desc = {};
+    desc.size = 256;
+    desc.stride = sizeof(float);
+    desc.bufferType = static_cast<uint32_t>(BufferType::Vertex);
+
+    RHIBuffer* buffer = GetDevice()->CreateBuffer(desc);
+    ASSERT_NE(buffer, nullptr);
+
+    EXPECT_EQ(buffer->GetState(), ResourceStates::Common);
+    buffer->SetState(ResourceStates::VertexAndConstantBuffer);
+    EXPECT_EQ(buffer->GetState(), ResourceStates::VertexAndConstantBuffer);
+
+    buffer->Shutdown();
+    delete buffer;
+}
+
+TEST_F(RHITestFixture, Buffer_Naming) {
+    BufferDesc desc = {};
+    desc.size = 256;
+    desc.stride = sizeof(float);
+    desc.bufferType = static_cast<uint32_t>(BufferType::Vertex);
+
+    RHIBuffer* buffer = GetDevice()->CreateBuffer(desc);
+    ASSERT_NE(buffer, nullptr);
+
+    buffer->SetName("TestBuffer");
+    EXPECT_EQ(buffer->GetName(), "TestBuffer");
+
+    buffer->Shutdown();
+    delete buffer;
+}
+
+TEST_F(RHITestFixture, Buffer_GetNativeHandle) {
+    BufferDesc desc = {};
+    desc.size = 256;
+    desc.stride = sizeof(float);
+    desc.bufferType = static_cast<uint32_t>(BufferType::Vertex);
+
+    RHIBuffer* buffer = GetDevice()->CreateBuffer(desc);
+    ASSERT_NE(buffer, nullptr);
+
+    EXPECT_NE(buffer->GetNativeHandle(), nullptr);
+
+    buffer->Shutdown();
+    delete buffer;
+}