add _run_subprocess-method and capture output line-by-line

tests/test_empty_output/test_empty_output.py

@@ -6,6 +6,27 @@
 non_verbose_file = os.path.join(here, "non_verbose.py")
 
 
+def _run_subprocess(script):
+    output = []
+    process = subprocess.Popen(
+        [sys.executable, "-u", script],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        text=True,
+        bufsize=1,  # Line buffered
+        env={**os.environ, "PYTHONUNBUFFERED": "1"},
+    )
+    # Read output line by line
+    while True:
+        line = process.stdout.readline()
+        if line:
+            output.append(line)
+        if not line and process.poll() is not None:
+            break
+
+    return "".join(output), process.stderr.read()
+
+
 def test_empty_output():
     output_verbose = subprocess.run(
         [sys.executable, "-u", verbose_file],
@@ -19,11 +40,11 @@ def test_empty_output():
         ["python", non_verbose_file], stdout=subprocess.PIPE
     )
 
-    verbose_str = output_verbose.stdout
-    non_verbose_str = output_non_verbose.stdout
+    stdout_verb, stderr_verb = _run_subprocess(verbose_file)
+    stdout_non_verb, stderr_non_verb = _run_subprocess(non_verbose_file)
 
-    print("\n verbose_str \n", verbose_str, "\n")
-    print("\n non_verbose_str \n", non_verbose_str, "\n")
+    print("\n stdout_verb \n", stdout_verb, "\n")
+    print("\n stderr_verb \n", stderr_verb, "\n")
 
-    assert "Results:" in verbose_str
-    assert not non_verbose_str
+    assert "Results:" in stdout_verb
+    assert not stdout_non_verb