diff --git a/test/test_prepare_outputs.py b/test/test_prepare_outputs.py
index 14a4976a..09481ed1 100644
--- a/test/test_prepare_outputs.py
+++ b/test/test_prepare_outputs.py
@@ -4,36 +4,36 @@
 
 
 def test_prepare_outputs_all_stdout():
-    output_prefix = "test_outputs"
+    output_prefix = "test_outputs_"
     with patch("duct.TeeStream") as mock_tee_stream, patch(
         "builtins.open", new_callable=MagicMock
     ) as mock_open:
         mock_tee_stream.return_value.start = MagicMock()
         stdout, stderr = prepare_outputs("all", "stdout", output_prefix)
-        mock_tee_stream.assert_called_with(f"{output_prefix}-stdout")
+        mock_tee_stream.assert_called_with(f"{output_prefix}stdout")
         assert stdout == mock_tee_stream.return_value
         assert stderr == mock_open.return_value
 
 
 def test_prepare_outputs_all_stderr():
-    output_prefix = "test_outputs"
+    output_prefix = "test_outputs_"
     with patch("duct.TeeStream") as mock_tee_stream, patch(
         "builtins.open", new_callable=MagicMock
     ) as mock_open:
         mock_tee_stream.return_value.start = MagicMock()
         stdout, stderr = prepare_outputs("all", "stderr", output_prefix)
-        mock_tee_stream.assert_called_with(f"{output_prefix}-stderr")
+        mock_tee_stream.assert_called_with(f"{output_prefix}stderr")
         assert stdout == mock_open.return_value
         assert stderr == mock_tee_stream.return_value
 
 
 def test_prepare_outputs_all_none():
-    output_prefix = "test_outputs"
+    output_prefix = "test_outputs_"
     with patch("builtins.open", new_callable=MagicMock) as mock_open:
         stdout, stderr = prepare_outputs("all", "none", output_prefix)
         calls = [
-            call(f"{output_prefix}-stdout"),
-            call(f"{output_prefix}-stderr"),
+            call(f"{output_prefix}stdout"),
+            call(f"{output_prefix}stderr"),
         ]
         mock_open.assert_has_calls(calls, any_order=True)
         assert stdout == mock_open.return_value
@@ -41,28 +41,28 @@ def test_prepare_outputs_all_none():
 
 
 def test_prepare_outputs_none_stdout():
-    output_prefix = "test_outputs"
+    output_prefix = "test_outputs_"
     stdout, stderr = prepare_outputs("none", "stdout", output_prefix)
     assert stdout == subprocess.PIPE
     assert stderr == subprocess.DEVNULL
 
 
 def test_prepare_outputs_none_stderr():
-    output_prefix = "test_outputs"
+    output_prefix = "test_outputs_"
     stdout, stderr = prepare_outputs("none", "stderr", output_prefix)
     assert stderr == subprocess.PIPE
     assert stdout == subprocess.DEVNULL
 
 
 def test_prepare_outputs_all_all():
-    output_prefix = "test_outputs"
+    output_prefix = "test_outputs_"
     with patch("duct.TeeStream") as mock_tee_stream:
         mock_tee_stream.return_value.start = MagicMock()
         stdout, stderr = prepare_outputs("all", "all", output_prefix)
         assert stdout == mock_tee_stream.return_value
         assert stderr == mock_tee_stream.return_value
         calls = [
-            call(f"{output_prefix}-stdout"),
-            call(f"{output_prefix}-stderr"),
+            call(f"{output_prefix}stdout"),
+            call(f"{output_prefix}stderr"),
         ]
         mock_tee_stream.assert_has_calls(calls, any_order=True)