add test

1. add test for non-1 step case
2. fix compatibility with 1.6

Author: N5N3

base/multidimensional.jl

@@ -621,16 +621,15 @@ module IteratorsMD
         size1 = size(piter, 1)
         vindʷ = only(iter.indices)
         vindᵒ = cld(first(vindʷ), size1) : cld(last(vindʷ), size1)
-        outer = @inbounds view(ci, vindᵒ)
         # Use Generator to make inner loop branchless
-        Base.Generator(Iterators.enumerate(outer)) do (i, I)
-            @inline
+        @inline function genouter(i::Int, I::CartesianIndex)
             l, r = first(vindᵒ), last(vindᵒ)
             skip = i == 1 ? first(vindʷ) - 1 - (l - 1) * size1 : 0
             len = i == length(vindᵒ) ? last(vindʷ) - (r - 1) * size1 : size1
-            len -= skip
-            skip, len, I
+            skip, len - skip, I
         end
+        outer = @inbounds view(ci, vindᵒ)
+        (genouter(i, I) for (i, I) in Iterators.enumerate(outer))
     end
     @inline simd_inner_length(iter::CartesianPartition, (skip, len, I)::Tuple{Int,Int,CartesianIndex}) = len
     @inline function simd_index(iter::CartesianPartition, (skip, len, I)::Tuple{Int,Int,CartesianIndex}, n::Int)

test/iterators.jl

@@ -548,12 +548,14 @@ end
                                                          (1,1), (8,8), (11, 13),
                                                          (1,1,1), (8, 4, 2), (11, 13, 17)),
                                                 part in (1, 7, 8, 11, 63, 64, 65, 142, 143, 144)
-    P = partition(CartesianIndices(dims), part)
-    for I in P
-        @test length(I) == iterate_length(I) == simd_iterate_length(I) == simd_trip_count(I)
-        @test collect(I) == iterate_elements(I) == simd_iterate_elements(I) == index_elements(I)
+    for iter in (CartesianIndices(dims), CartesianIndices(map(d -> 1:2:2d, dims))) 
+        P = partition(iter, part)
+        for I in P
+            @test length(I) == iterate_length(I) == simd_iterate_length(I) == simd_trip_count(I)
+            @test collect(I) == iterate_elements(I) == simd_iterate_elements(I) == index_elements(I)
+        end
+        @test all(Base.splat(==), zip(Iterators.flatten(map(collect, P)), iter))
     end
-    @test all(Base.splat(==), zip(Iterators.flatten(map(collect, P)), CartesianIndices(dims)))
 end
 @testset "empty/invalid partitions" begin
     @test_throws ArgumentError partition(1:10, 0)