add a test

test/runtests.jl

@@ -1015,5 +1015,27 @@ end
 
         # end
 
+        @testset "# 493" begin
+            # This test stresses the existence of the mechanism
+            # implemented in https://github.com/apache/arrow-julia/pull/493,
+            # but doesn't stress the actual use case that motivates
+            # that mechanism, simply because it'd be more annoying to
+            # write that test; see the PR for details.
+            struct Foo493
+                x::Int
+                y::Int
+            end
+            Arrow.ArrowTypes.arrowname(::Type{Foo493}) = Symbol("JuliaLang.Foo493")
+            Arrow.ArrowTypes.JuliaType(::Val{Symbol("JuliaLang.Foo493")}, T) = Foo493
+            function Arrow.ArrowTypes.fromarrow(::Type{Foo493}, f::Arrow.StructElement)
+                return Foo493(f.fields.x + 1, f.fields.y + 1)
+            end
+            t = (; f=[Foo493(1, 2), Foo493(3, 4)])
+            buf = Arrow.tobuffer(t)
+            tbl = Arrow.Table(buf)
+            @test tbl.f[1] === Foo493(2, 3)
+            @test tbl.f[2] === Foo493(4, 5)
+        end
+
     end # @testset "misc"
 end