test(xCAT-test): cover the riscv64 Ubuntu network drivers

Reads the list imgutils returns. Covers the drivers a node needs to reach
its root filesystem, the overlay module, the architectures that already
worked keeping theirs, and an unknown architecture still getting an empty
list.

Signed-off-by: Vinícius Ferrão <2031761+viniciusferrao@users.noreply.github.com>

xCAT-test/unit/ubuntu_riscv64_net_drivers.t

@@ -0,0 +1,38 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+
+use FindBin;
+use Test::More;
+
+# Without a driver list the Ubuntu netboot image ships no network module at all, and a node
+# whose NIC is not built into the kernel cannot reach its root filesystem. QEMU hides this,
+# because virtio-net is built into the Ubuntu riscv64 kernel; a machine with an r8169 or an
+# e1000e does not boot.
+
+use lib "$FindBin::Bin/../../perl-xCAT";
+use lib "$FindBin::Bin/../../xCAT-server/lib/perl";
+use lib "$FindBin::Bin/../../xCAT-server/share/xcat/netboot/imgutils";
+require imgutils;
+
+my @riscv = imgutils::default_net_drivers( 'ubuntu', 'riscv64' );
+ok( scalar @riscv, 'a riscv64 Ubuntu image is given network drivers' );
+
+for my $driver (qw(virtio_net e1000 e1000e igb r8169 tg3 mlx5_core)) {
+    ok( scalar( grep { $_ eq $driver } @riscv ), "the list carries $driver" );
+}
+
+# Every Ubuntu row carries overlay, because the netboot root is an overlay mount.
+ok( scalar( grep { $_ eq 'overlay' } @riscv ), 'the list carries overlay' );
+
+# The architectures that already worked must keep the drivers they had.
+is_deeply(
+    [ imgutils::default_net_drivers( 'ubuntu', 'x86_64' ) ],
+    [qw(tg3 bnx2 bnx2x e1000 e1000e igb mlx_en mlx5_core virtio_net overlay)],
+    'x86_64 keeps its drivers' );
+ok( scalar( imgutils::default_net_drivers( 'ubuntu', 'ppc64el' ) ),
+    'ppc64el keeps its drivers' );
+is_deeply( [ imgutils::default_net_drivers( 'ubuntu', 'sparc' ) ], [],
+    'an architecture with no entry still gets an empty list' );
+
+done_testing();