diff --git a/test/test_tailpipe.py b/test/test_tailpipe.py
index 1f363ccc..0f082091 100644
--- a/test/test_tailpipe.py
+++ b/test/test_tailpipe.py
@@ -6,7 +6,8 @@
 from utils import MockStream
 from duct import TailPipe
 
-FIXTURE_LIST = [f"ten_{i}" for i in range(1, 7)]
+# 10^7 line fixture is about 70MB
+FIXTURE_LIST = [f"ten_{i}" for i in range(1, 8)]
 
 
 @pytest.fixture(scope="module", params=FIXTURE_LIST)
@@ -14,11 +15,11 @@ def fixture_path(request, tmp_path_factory):
     num_lines_exponent = int(request.param.split("_")[1])
     base_temp_dir = tmp_path_factory.mktemp("fixture_data")
     file_path = base_temp_dir / f"{request.param}.txt"
-    print(f"Creating fixture for {num_lines_exponent}")
-    print(f"10 ^ {num_lines_exponent}: {10 ** num_lines_exponent}")
     with open(file_path, "w") as f:
         for i in range(10**num_lines_exponent):
             f.write(f"{i}\n")
+    # print(f"10 ^ {num_lines_exponent}: {10 ** num_lines_exponent}")
+    # print(f"Fixture file size: {os.path.getsize(file_path)} bytes")
     yield str(file_path)
 
     os.remove(file_path)
@@ -26,7 +27,7 @@ def fixture_path(request, tmp_path_factory):
 
 @pytest.mark.parametrize("fixture_path", FIXTURE_LIST, indirect=True)
 @patch("sys.stdout", new_callable=lambda: MockStream())
-def test_high_throughput(mock_stdout, fixture_path):
+def test_high_throughput_stdout(mock_stdout, fixture_path):
     with tempfile.NamedTemporaryFile(mode="wb") as tmpfile:
         process = subprocess.Popen(
             ["cat", fixture_path],
@@ -43,6 +44,26 @@ def test_high_throughput(mock_stdout, fixture_path):
     assert mock_stdout.getvalue() == expected
 
 
+@pytest.mark.parametrize("fixture_path", FIXTURE_LIST, indirect=True)
+@patch("sys.stderr", new_callable=lambda: MockStream())
+def test_high_throughput_stderr(mock_stderr, fixture_path):
+    with tempfile.NamedTemporaryFile(mode="wb") as tmpfile:
+        process = subprocess.Popen(
+            ["./test/cat_to_err.py", fixture_path],
+            stdout=subprocess.DEVNULL,
+            stderr=tmpfile,
+        )
+        stream = TailPipe(tmpfile.name, mock_stderr.buffer)
+        stream.start()
+        process.wait()
+        stream.close()
+
+    assert process.returncode == 0
+    with open(fixture_path, "rb") as fixture:
+        expected = fixture.read()
+    assert mock_stderr.getvalue() == expected
+
+
 @patch("sys.stdout", new_callable=lambda: MockStream())
 def test_close(mock_stdout):
     with tempfile.NamedTemporaryFile(mode="wb") as tmpfile:
@@ -50,7 +71,3 @@ def test_close(mock_stdout):
         stream.start()
         stream.close()
         assert stream.infile.closed
-
-
-if __name__ == "__main__":
-    test_high_throughput()
diff --git a/tox.ini b/tox.ini
index d2d7530c..d74292de 100644
--- a/tox.ini
+++ b/tox.ini
@@ -33,7 +33,6 @@ commands =
     mypy src test
 
 [pytest]
-addopts = --cov=duct --no-cov-on-fail
 filterwarnings = error
 norecursedirs = test/data
 markers =