diff --git a/pyproject.toml b/pyproject.toml
index 845d6c98..b6d833db 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -107,7 +107,7 @@ build-backend = "setuptools.build_meta"
 packages = ["xcp", "xcp.net", "xcp.net.ifrename"]
 
 [tool.black]
-line-length = 96
+line-length = 92
 
 [tool.mypy]
 pretty = true
diff --git a/tests/test_ifrename_dynamic.py b/tests/test_ifrename_dynamic.py
index 4a20b965..e3b45a64 100644
--- a/tests/test_ifrename_dynamic.py
+++ b/tests/test_ifrename_dynamic.py
@@ -24,12 +24,15 @@ def tearDown(self):
         self.logbuf.close()
 
     def test_null(self):
+        self.assertLoadDynamicRules("")
 
-        fd = StringIO("")
-        dr = DynamicRules(fd=fd)
-
+    def loadDynamicRules(self, rules):
+        dr = DynamicRules(fd=StringIO(rules))
         self.assertTrue(dr.load_and_parse())
+        return dr
 
+    def assertLoadDynamicRules(self, rules):
+        dr = self.loadDynamicRules(rules)
         self.assertEqual(dr.lastboot, [])
         self.assertEqual(dr.old, [])
 
@@ -46,40 +49,21 @@ def test_empty(self):
         self.assertEqual(dr.old, [])
 
     def test_one_invalid(self):
-
-        fd = StringIO(
-            '{"lastboot":[["","",""]],"old":[]}'
-            )
-        dr = DynamicRules(fd=fd)
-
-        self.assertTrue(dr.load_and_parse())
-
-        self.assertEqual(dr.lastboot, [])
-        self.assertEqual(dr.old, [])
+        self.assertLoadDynamicRules('{"lastboot":[["","",""]],"old":[]}')
 
     def test_one_valid_lastboot(self):
-
-        fd = StringIO(
+        dr = self.loadDynamicRules(
             '{"lastboot":[["01:23:45:67:89:0a","00:10.2","eth2"]],"old":[]}'
-            )
-        dr = DynamicRules(fd=fd)
-
-        self.assertTrue(dr.load_and_parse())
-
-        self.assertEqual(dr.lastboot,
-                         [MACPCI("01:23:45:67:89:0a","00:10.2", tname="eth2")])
+        )
+        self.assertEqual(
+            dr.lastboot, [MACPCI("01:23:45:67:89:0a", "00:10.2", tname="eth2")]
+        )
         self.assertEqual(dr.old, [])
 
-
     def test_one_valid_lastboot2(self):
-
-        fd = StringIO(
+        dr = self.loadDynamicRules(
             '{"lastboot":[],"old":[["01:23:45:67:89:0a","00:10.2","eth2"]]}'
-            )
-        dr = DynamicRules(fd=fd)
-
-        self.assertTrue(dr.load_and_parse())
-
+        )
         self.assertEqual(dr.lastboot, [])
         self.assertEqual(dr.old,
                          [MACPCI("01:23:45:67:89:0a","00:10.2", tname="eth2")])