diff --git a/test/basetest/exceptions.py b/test/basetest/exceptions.py
index f1f753109..998a24325 100644
--- a/test/basetest/exceptions.py
+++ b/test/basetest/exceptions.py
@@ -3,11 +3,12 @@ import signal
 
 
 class CommandError(Exception):
-    def __init__(self, cmd, code, out, err, msg=None):
+    def __init__(self, cmd, code, out, err=None, msg=None):
         if msg is None:
-            msg_suffix = (
-                "\n*** Start STDOUT ***\n{2}\n*** End STDOUT ***\n"
-                "\n*** Start STDERR ***\n{3}\n*** End STDERR ***\n"
+            msg_suffix = "\n*** Start STDOUT ***\n{2}\n*** End STDOUT ***\n"
+            if err is not None:
+                msg_suffix += (
+                    "\n*** Start STDERR ***\n{3}\n*** End STDERR ***\n"
                 )
             if code == -signal.SIGABRT:
                 self.msg = ("Command '{0}' was aborted, likely due to not "
diff --git a/test/basetest/task.py b/test/basetest/task.py
index 060f0f63a..a06c84498 100644
--- a/test/basetest/task.py
+++ b/test/basetest/task.py
@@ -256,7 +256,7 @@ class Task(object):
         cmd = (self.taskw, "config", "--", var, value)
         return run_cmd_wait(cmd, env=self.env)
 
-    def runSuccess(self, args=(), input=None, merge_streams=True,
+    def runSuccess(self, args=(), input=None, merge_streams=False,
                    timeout=1):
         """Invoke task with given arguments and fail if exit code != 0
 
@@ -272,7 +272,8 @@ class Task(object):
         timeout = number of seconds the test will wait for every task call.
         Defaults to 1 second if not specified. Unit is seconds.
 
-        Returns (exit_code, stdout, stderr)
+        Returns (exit_code, stdout, stderr) if merge_streams=False
+                (exit_code, output) if merge_streams=True
         """
         # Create a copy of the command
         command = self._command[:]
@@ -288,7 +289,7 @@ class Task(object):
 
         return output
 
-    def runError(self, args=(), input=None, merge_streams=True, timeout=1):
+    def runError(self, args=(), input=None, merge_streams=False, timeout=1):
         """Invoke task with given arguments and fail if exit code == 0
 
         Use runSuccess if you want exit_code to be tested automatically and
@@ -303,7 +304,8 @@ class Task(object):
         timeout = number of seconds the test will wait for every task call.
         Defaults to 1 second if not specified. Unit is seconds.
 
-        Returns (exit_code, stdout, stderr)
+        Returns (exit_code, stdout, stderr) if merge_streams=False
+                (exit_code, output) if merge_streams=True
         """
         # Create a copy of the command
         command = self._command[:]
diff --git a/test/basetest/utils.py b/test/basetest/utils.py
index 2cc86f5ef..804e35ae9 100644
--- a/test/basetest/utils.py
+++ b/test/basetest/utils.py
@@ -13,7 +13,7 @@ try:
     import simplejson as json
 except ImportError:
     import json
-from .exceptions import CommandError, TimeoutWaitingForStream, StreamsAreMerged
+from .exceptions import CommandError, TimeoutWaitingForStream
 
 USED_PORTS = set()
 ON_POSIX = 'posix' in sys.builtin_module_names
@@ -133,15 +133,16 @@ def run_cmd_wait(cmd, input=None, stdout=PIPE, stderr=PIPE,
               close_fds=ON_POSIX, env=env)
     out, err, exit = _get_output(p, input, timeout)
 
-    # If streams were merged err should always be None so represent it with a
-    # more informative object
     if merge_streams:
-        err = StreamsAreMerged()
-
-    if exit != 0:
-        raise CommandError(cmd, exit, out, err)
-
-    return exit, out, err
+        if exit != 0:
+            raise CommandError(cmd, exit, out)
+        else:
+            return exit, out
+    else:
+        if exit != 0:
+            raise CommandError(cmd, exit, out, err)
+        else:
+            return exit, out, err
 
 
 def run_cmd_wait_nofail(*args, **kwargs):
diff --git a/test/tw-1441.t b/test/tw-1441.t
index 54f67484d..57d184163 100755
--- a/test/tw-1441.t
+++ b/test/tw-1441.t
@@ -17,7 +17,7 @@ class TestBug1441(TestCase):
     def test_import_filename(self):
         """import fails if file doesn't exist"""
         command = ("import", "xxx_doesnotexist")
-        code, out, err = self.t.runError(command, merge_streams=False)
+        code, out, err = self.t.runError(command)
 
         self.assertIn("File 'xxx_doesnotexist' not found.", err)