Add tests for gpu_backend!

test/cuda.jl

@@ -1,4 +1,4 @@
-using LuxDeviceUtils, Random
+using LuxDeviceUtils, Random, Functors
 using ArrayInterface: parameterless_type
 
 @testset "CPU Fallback" begin
@@ -91,7 +91,15 @@ using FillArrays, Zygote  # Extensions
         @test ps_cpu.farray isa Fill
     end
 
-    ps_mixed = (; a=rand(2), b=device(rand(2)))
+    struct MyStruct
+        x
+    end
+
+    Functors.@functor MyStruct
+
+    ps_mixed = (; a=rand(2), c=(rand(2), 1), st=MyStruct(rand(2)), b=device(rand(2)))
+    @test get_device(ps_mixed.st) isa LuxCPUDevice
+    @test get_device(ps_mixed.c) isa LuxCPUDevice
     @test_throws ArgumentError get_device(ps_mixed)
 
     dev = gpu_device()

test/misc.jl

@@ -106,3 +106,26 @@ end
     @test get_device(x) isa LuxCPUDevice
     @test get_device(x_view) isa LuxCPUDevice
 end
+
+@testset "loaded and functional" begin
+    @test LuxDeviceUtils.loaded(LuxCPUDevice)
+    @test LuxDeviceUtils.functional(LuxCPUDevice)
+end
+
+@testset "writing to preferences" begin
+    @test_logs (:info,
+        "Deleted the local preference for `gpu_backend`. Restart Julia to use the new backend.") gpu_backend!()
+
+    for backend in (:CUDA, :AMDGPU, :oneAPI, :Metal, LuxAMDGPUDevice(),
+        LuxCUDADevice(), LuxMetalDevice(), LuxoneAPIDevice())
+        backend_name = backend isa Symbol ? string(backend) :
+                       LuxDeviceUtils._get_device_name(backend)
+        @test_logs (:info,
+            "GPU backend has been set to $(backend_name). Restart Julia to use the new backend.") gpu_backend!(backend)
+    end
+
+    gpu_backend!(:CUDA)
+    @test_logs (:info, "GPU backend is already set to CUDA. No action is required.") gpu_backend!(:CUDA)
+
+    @test_throws ArgumentError gpu_backend!("my_backend")
+end