A few missing indices tests (#31706)

* Missing IndexStyle tests

* promote_shape for Tuples/Dims

Author: kshyatt

test/abstractarray.jl

@@ -970,3 +970,20 @@ end
     @test get(11:15, CartesianIndex(6), nothing) === nothing
     @test get(11:15, CartesianIndex(5), nothing) === 15
 end
+
+@testset "IndexStyle for various types" begin
+    @test Base.IndexStyle(UpperTriangular) == IndexCartesian() # subtype of AbstractArray, not of Array
+    @test Base.IndexStyle(Vector) == IndexLinear()
+    @test Base.IndexStyle(UnitRange) == IndexLinear()
+    @test Base.IndexStyle(UpperTriangular(rand(3, 3)), [1; 2; 3]) == IndexCartesian()
+    @test Base.IndexStyle(UpperTriangular(rand(3, 3)), rand(3, 3), [1; 2; 3]) == IndexCartesian()
+    @test Base.IndexStyle(rand(3, 3), [1; 2; 3]) == IndexLinear()
+end
+
+@testset "promote_shape for Tuples and Dims" begin
+    @test promote_shape((2, 1), (2,)) == (2, 1)
+    @test_throws DimensionMismatch promote_shape((2, 3), (2,))
+    @test promote_shape(Dims((2, 1)), Dims((2,))) == (2, 1)
+    @test_throws DimensionMismatch promote_shape(Dims((2, 2)), Dims((2,)))
+    @test_throws DimensionMismatch promote_shape(Dims((2, 3, 1)), Dims((2,2)))
+end