[PATCH 2/3] Acceptance tests: introduce utility method for tags unique vals

[Cleber Rosa <crosa@redhat.com>]

Currently a test can describe the target architecture binary that it
should primarily be run with, be setting a single tag value.

The same approach is expected to be done with other QEMU aspects to be
tested, for instance, the machine type and accelerator, so let's
generalize the logic into a utility method.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
---
 tests/acceptance/avocado_qemu/__init__.py | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/tests/acceptance/avocado_qemu/__init__.py b/tests/acceptance/avocado_qemu/__init__.py
index bd41e0443c..02775bafcf 100644
--- a/tests/acceptance/avocado_qemu/__init__.py
+++ b/tests/acceptance/avocado_qemu/__init__.py
@@ -54,14 +54,21 @@ def pick_default_qemu_bin(arch=None):
 
 
 class Test(avocado.Test):
+    def _get_unique_tag_val(self, tag_name):
+        """
+        Gets a tag value, if unique for a key
+        """
+        vals = self.tags.get(tag_name, [])
+        if len(vals) == 1:
+            return vals.pop()
+        return None
+
     def setUp(self):
         self._vms = {}
-        arches = self.tags.get('arch', [])
-        if len(arches) == 1:
-            arch = arches.pop()
-        else:
-            arch = None
-        self.arch = self.params.get('arch', default=arch)
+
+        self.arch = self.params.get('arch',
+                                    default=self._get_unique_tag_val('arch'))
+
         default_qemu_bin = pick_default_qemu_bin(arch=self.arch)
         self.qemu_bin = self.params.get('qemu_bin',
                                         default=default_qemu_bin)
-- 
2.21.0