kernel: fix check in OutNeighbours

[james-d-mitchell]

This PR fixes Issue #518.

[wilfwilson]

Cheers

[james-d-mitchell]

The CI fails because of some issues with the wording of errors, any idea how I can add this test and get around this @wilfwilson ?

Error, expected a digraph, not a homogeneous plain list
Error, expected a digraph, not a list (plain,hom)

[wilfwilson]

I've pushed a slightly different test, I hope you don't mind. If you do OutNeighbours(OutNeighbours) then you get a consistent error message across GAP versions:

Error, expected a digraph, not a function

Once we require GAP 4.11, these kinds of problems will be straightforward to work around because you can use the syntax #@if, #@else, and #@endif in test files to test stuff conditionally, and to expect different outputs.

[james-d-mitchell]

I've pushed a slightly different test, I hope you don't mind.

Thanks!

Once we require GAP 4.11, these kinds of problems will be straightforward to work around because you can use the syntax #@if, #@else, and #@endif in test files to test stuff conditionally, and to expect different outputs.

I didn't know this! Awesome!