Add backend tests

Author: gaurav-arya

test/runtests.jl

@@ -595,6 +595,11 @@ end
     end # x
 end
 
+@testset "AbstractFFTs FFT backend tests" begin
+    AbstractFFTs.TestUtils.test_complex_ffts(Array)
+    AbstractFFTs.TestUtils.test_real_ffts(Array; copy_input=true)
+end
+
 @testset "ChainRules" begin
 
 end