[PATCH 14/27] tasst: Add helper to get network interface names for a site

Start adding convenience functions for handling sites as places with
network setup with a simple helper which lists the network interface names
for a site.

Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>

# Conflicts:
#	test/tasst/exesite.py
---
 test/tasst/exesite.py | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/test/tasst/exesite.py b/test/tasst/exesite.py
index e69db8ad..811b670e 100644
--- a/test/tasst/exesite.py
+++ b/test/tasst/exesite.py
@@ -13,10 +13,13 @@ tasst/exesite.py - Manage simulated network sites for testing
 
 
 import contextlib
+import json
 
 import avocado
 from avocado.utils.process import CmdError
-from avocado_classless.test import assert_eq, assert_raises, test_output
+from avocado_classless.test import (
+    assert_eq, assert_in, assert_raises, test_output
+)
 
 from tasst.typecheck import typecheck
 
@@ -93,6 +96,11 @@ class Site(contextlib.AbstractContextManager):
             raise avocado.TestCancel(
                 f"Missing commands {', '.join(missing)} on
{self.name}")
 
+    def ifs(self):
+        self.require_cmds('ip')
+        info = json.loads(self.output('ip -j link show'))
+        return [i['ifname'] for i in info]
+
 
 def test_site(sitefn):
     def test_true(s):
@@ -143,9 +151,14 @@ def test_site(sitefn):
                          ignore_status=True):
                 pass
 
+    def test_has_lo(s):
+        with s as site:
+            assert_in('lo', site.ifs())
+
     return test_output(test_true, test_false, test_echo, test_timeout,
                        test_bg_true, test_bg_false, test_bg_echo,
-                       test_bg_timeout, test_bg_context_timeout)(sitefn)
+                       test_bg_timeout, test_bg_context_timeout,
+                       test_has_lo)(sitefn)
 
 
 class RealHost(Site):
-- 
2.41.0