feat: Support reading file_or_dir args from a file

Author: levsa

AUTHORS

@@ -235,6 +235,7 @@ Kyle Altendorf
 Lawrence Mitchell
 Lee Kamentsky
 Lev Maximov
+Levon Saldamli
 Lewis Cowles
 Llandy Riveron Del Risco
 Loic Esteve

changelog/11871.feature.rst

@@ -0,0 +1,4 @@
+Added support for reading ``file_or_dir`` positional arguments from a file
+using the prefix character '@', like e.g.:
+
+``pytest @tests.txt``

src/_pytest/config/argparsing.py

@@ -415,6 +415,7 @@ def __init__(
             add_help=False,
             formatter_class=DropShorterLongHelpFormatter,
             allow_abbrev=False,
+            fromfile_prefix_chars="@",
         )
         # extra_info is a dict of (param -> value) to display if there's
         # an usage error to provide more contextual information to the user.

testing/test_parseopt.py

@@ -125,6 +125,13 @@ def test_parse2(self, parser: parseopt.Parser) -> None:
         args = parser.parse([Path(".")])
         assert getattr(args, parseopt.FILE_OR_DIR)[0] == "."
 
+    def test_parse_from_file(self, parser: parseopt.Parser, tmp_path: Path) -> None:
+        tests = [".", "some.py::Test::test_method[param0]", "other/test_file.py"]
+        test_file = tmp_path / "tests.txt"
+        test_file.write_text("\n".join(tests), encoding="utf-8")
+        args = parser.parse([f"@{test_file.absolute()}"])
+        assert getattr(args, parseopt.FILE_OR_DIR) == tests
+
     def test_parse_known_args(self, parser: parseopt.Parser) -> None:
         parser.parse_known_args([Path(".")])
         parser.addoption("--hello", action="store_true")