diff --git a/bin/tests/system/checkds/tests_checkds.py b/bin/tests/system/checkds/tests_checkds.py
index b411282d36..f369f2e3fb 100755
--- a/bin/tests/system/checkds/tests_checkds.py
+++ b/bin/tests/system/checkds/tests_checkds.py
@@ -312,9 +312,11 @@ def dspublished_tests(checkds, addr):
         CheckDSTest(
             zone=f"bad.{checkds}.dspublish.ns6",
             logs_to_wait_for=(
-                "bad DS response from 10.53.0.6"
-                if checkds == "explicit"
-                else "error during parental-agents processing",
+                (
+                    "bad DS response from 10.53.0.6"
+                    if checkds == "explicit"
+                    else "error during parental-agents processing"
+                ),
             ),
             expected_parent_state="!DSPublish",
         ),
@@ -394,9 +396,11 @@ def dswithdrawn_tests(checkds, addr):
         CheckDSTest(
             zone=f"bad.{checkds}.dsremoved.ns6",
             logs_to_wait_for=(
-                "bad DS response from 10.53.0.6"
-                if checkds == "explicit"
-                else "error during parental-agents processing",
+                (
+                    "bad DS response from 10.53.0.6"
+                    if checkds == "explicit"
+                    else "error during parental-agents processing"
+                ),
             ),
             expected_parent_state="!DSRemoved",
         ),
diff --git a/bin/tests/system/isctest/instance.py b/bin/tests/system/isctest/instance.py
index ede48c095c..c559b0a605 100644
--- a/bin/tests/system/isctest/instance.py
+++ b/bin/tests/system/isctest/instance.py
@@ -27,7 +27,6 @@ class NamedPorts(NamedTuple):
 
 
 class NamedInstance:
-
     """
     A class representing a `named` instance used in a system test.
 
diff --git a/bin/tests/system/isctest/log.py b/bin/tests/system/isctest/log.py
index 8a382626c0..9f1b90ba25 100644
--- a/bin/tests/system/isctest/log.py
+++ b/bin/tests/system/isctest/log.py
@@ -57,7 +57,6 @@ class LogFile:
 
 
 class WatchLog(abc.ABC):
-
     """
     Wait for a log message to appear in a text file.
 
@@ -294,19 +293,18 @@ class WatchLogFromHere(WatchLog):
 
 # pylint: disable=too-few-public-methods
 class RNDCExecutor(abc.ABC):
-
     """
     An interface which RNDC executors have to implement in order for the
     `NamedInstance` class to be able to use them.
     """
 
     @overload
-    def call(self, ip: str, port: int, command: str, timeout: int = 10) -> str:
-        ...
+    def call(self, ip: str, port: int, command: str, timeout: int = 10) -> str: ...
 
     @overload
-    def call(self, ip: str, port: int, command: List[str], timeout: int = 10) -> str:
-        ...
+    def call(
+        self, ip: str, port: int, command: List[str], timeout: int = 10
+    ) -> str: ...
 
     @abc.abstractmethod
     def call(
@@ -326,7 +324,6 @@ class RNDCException(Exception):
 
 
 class RNDCBinaryExecutor(RNDCExecutor):
-
     """
     An `RNDCExecutor` which sends RNDC commands to servers using the `rndc`
     binary.
@@ -342,12 +339,12 @@ class RNDCBinaryExecutor(RNDCExecutor):
         self._base_cmdline = [rndc_path, "-c", rndc_conf]
 
     @overload
-    def call(self, ip: str, port: int, command: str, timeout: int = 10) -> str:
-        ...
+    def call(self, ip: str, port: int, command: str, timeout: int = 10) -> str: ...
 
     @overload
-    def call(self, ip: str, port: int, command: List[str], timeout: int = 10) -> str:
-        ...
+    def call(
+        self, ip: str, port: int, command: List[str], timeout: int = 10
+    ) -> str: ...
 
     def call(
         self, ip: str, port: int, command: Union[str, List[str]], timeout: int = 10
diff --git a/bin/tests/system/isctest/rndc.py b/bin/tests/system/isctest/rndc.py
index 3accc369dc..6e869ab316 100644
--- a/bin/tests/system/isctest/rndc.py
+++ b/bin/tests/system/isctest/rndc.py
@@ -16,7 +16,6 @@ import subprocess
 
 # pylint: disable=too-few-public-methods
 class RNDCExecutor(abc.ABC):
-
     """
     An interface which RNDC executors have to implement in order for the
     `NamedInstance` class to be able to use them.
@@ -38,7 +37,6 @@ class RNDCException(Exception):
 
 
 class RNDCBinaryExecutor(RNDCExecutor):
-
     """
     An `RNDCExecutor` which sends RNDC commands to servers using the `rndc`
     binary.