Add upstream tests

Author: gaurav-arya

test/Project.toml

@@ -1,8 +1,8 @@
-# A bug in Julia 1.6.0's Pkg causes Preferences to be dropped during `Pkg.test()`, so we work around
-# it by explicitly creating a `test/Project.toml` which will correctly communicate any preferences
-# through to the child Julia process.  X-ref: https://github.com/JuliaLang/Pkg.jl/issues/2500
-
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"
+ChainRulesTestUtils = "cdddcdb0-9152-4a09-a978-84456f9df70a"
+FiniteDifferences = "26cc04aa-876d-5657-8c51-4c34ba976000"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
+Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+Unitful = "1986cc42-f94f-5a68-af5c-568840ba703d"

test/runtests.jl

@@ -539,3 +539,9 @@ end
     end
     @test FFTW.get_num_threads() == 2 # Unchanged
 end
+
+@testset "AbstractFFTs upstream tests" begin
+    include(joinpath(pathof(AbstractFFTs), "..", "..", "test", "testbackend.jl"))
+    using .AbstractFFTsTestUtils
+    test_fft_backend()
+end