Make use of capsys fixture in test

tests/link/c/test_cmodule.py

@@ -9,8 +9,6 @@
 import os
 import sys
 import tempfile
-from contextlib import redirect_stderr, redirect_stdout
-from io import StringIO
 from unittest.mock import patch
 
 import numpy as np
@@ -219,14 +217,11 @@ def mocked_blas_opt(*args, **kwargs):
 
 
 @patch("numpy.distutils.system_info.get_info", new=mocked_blas_opt)
-def test_blas_opt_warnings():
-    sio_out = StringIO()
-    sio_err = StringIO()
-    with redirect_stdout(sio_out):
-        with redirect_stderr(sio_err):
-            default_blas_ldflags()
-    stdout_lines = sio_out.getvalue().splitlines()
-    stderr_lines = sio_err.getvalue().splitlines()
+def test_blas_opt_warnings(capsys):
+    default_blas_ldflags()
+    captured_messages = capsys.readouterr()
+    stdout_lines = captured_messages.out.splitlines()
+    stderr_lines = captured_messages.err.splitlines()
     assert stdout_lines == [
         "This line will be re-printed to stdout",
         "Could not locate executable foo: this line will be re-printed to stdout",