fix testing to not include all backends automatically

test/runtests.jl

@@ -1,36 +1,47 @@
 using DistanceTransforms
 using Test
 
-using KernelAbstractions
-using CUDA, AMDGPU, Metal
-using oneAPI
-using Random
+AVAILABLE_GPU_BACKENDS = ["CUDA", "AMDGPU", "Metal", "oneAPI"]
+TEST_BACKENDS = filter(x->x in [AVAILABLE_GPU_BACKENDS; "CPU"], ARGS)
+
+if isempty(TEST_BACKENDS)
+    using Preferences
+    TEST_BACKENDS = [load_preference(KomaMRICore, "test_backend", "CPU")]
+    @info "Using [preferences.KomaMRICore]." backend=first(TEST_BACKENDS)
+else
+    @info "Using test_args" backend=first(TEST_BACKENDS)
+end
+
+USE_GPU = any(AVAILABLE_GPU_BACKENDS .∈ Ref(TEST_BACKENDS))
 
-if CUDA.functional()
-    @info "Using CUDA"
+if "CUDA" in TEST_BACKENDS
+    using CUDA
     CUDA.versioninfo()
     backend = CUDABackend()
     dev = CuArray
-elseif AMDGPU.functional()
-    @info "Using AMD"
+elseif "AMDGPU" in TEST_BACKENDS
+    using AMDGPU
     AMDGPU.versioninfo()
     backend = ROCBackend()
     dev = ROCArray
-elseif oneAPI.functional() ## not well supported
-    @info "Using oneAPI"
-    oneAPI.versioninfo()
-    backend = oneBackend()
-    dev = oneArray
-elseif Metal.functional()
-    @info "Using Metal"
+elseif "Metal" in TEST_BACKENDS
+    using Metal
     Metal.versioninfo()
     backend = MetalBackend()
     dev = MtlArray
+elseif "oneAPI" in TEST_BACKENDS
+    using oneAPI
+    oneAPI.versioninfo()
+    backend = oneBackend()
+    dev = oneArray
 else
-    @info "No GPU is available. Using CPU."
+    @info "CPU using $(Threads.nthreads()) thread(s)" maxlog=1
     backend = CPU()
     dev = Array
 end
 
+using KernelAbstractions
+using Random
+
 include("transform.jl")
 include("utils.jl")