test(xcat-core): capture the SUSE NIC backup that hides a copy failure

nic_cfg.sh backup ends its SUSE branch with "|| :" and sends stderr to
/dev/null. A cp that fails on a real ifcfg file therefore returns 0 and
prints nothing, and the restore later puts back an incomplete backup.

The new cases check that a directory with no ifcfg file still backs up,
that an ifcfg file is copied, and that a failed copy returns non-zero
with the cp error on stderr. The last case fails on the current script.

Signed-off-by: Daniel Hilst <392820+dhilst@users.noreply.github.com>

xCAT-test/bats/nic_cfg_backup_absent_dir.bats

@@ -1,6 +1,8 @@
 #!/usr/bin/env bats
 # nic_cfg.sh backup must succeed on a node with no persistent network configuration.
 
+bats_require_minimum_version 1.5.0
+
 load 'helpers/shell_source'
 
 setup()
@@ -51,3 +53,31 @@ setup()
     NIC_CFG_BACKEND=ubuntu run "$SCRIPT" backup
     [ "$status" -ne 0 ]
 }
+
+@test "a SUSE node with no ifcfg file is backed up without an error and nothing copied" {
+    mkdir -p "$SUSEDIR"
+    printf 'default 192.0.2.1 - -\n' >"$SUSEDIR/routes"
+    NIC_CFG_BACKEND=suse run "$SCRIPT" backup
+    [ "$status" -eq 0 ]
+    [ -z "$(ls -A "$BACKUP")" ]
+}
+
+@test "a SUSE node has its ifcfg files backed up" {
+    mkdir -p "$SUSEDIR"
+    printf "BOOTPROTO='static'\n" >"$SUSEDIR/ifcfg-eth0"
+    NIC_CFG_BACKEND=suse run "$SCRIPT" backup
+    [ "$status" -eq 0 ]
+    [ -f "$BACKUP/ifcfg-eth0" ]
+}
+
+@test "a SUSE ifcfg file that cannot be copied fails the backup" {
+    mkdir -p "$SUSEDIR"
+    printf "BOOTPROTO='static'\n" >"$SUSEDIR/ifcfg-eth0"
+    # nic_cfg.sh is a bash script, so it inherits this exported function.
+    cp() { echo "cp: cannot create regular file: Read-only file system" >&2; return 1; }
+    export -f cp
+    NIC_CFG_BACKEND=suse run --separate-stderr "$SCRIPT" backup
+    unset -f cp
+    [ "$status" -ne 0 ]
+    [[ "$stderr" == *"Read-only file system"* ]]
+}