pytester: testdir: add makefiles helper

This is a sane method to create a set of files, allowing for absolute
paths.

Ref: #6578
Ref: #6579

Author: blueyed

src/_pytest/pytester.py

@@ -7,6 +7,7 @@
 import re
 import subprocess
 import sys
+import textwrap
 import time
 import traceback
 from fnmatch import fnmatch
@@ -674,6 +675,31 @@ def maketxtfile(self, *args, **kwargs):
         """Shortcut for .makefile() with a .txt extension."""
         return self._makefile(".txt", args, kwargs)
 
+    def makefiles(
+        self, files: Dict[str, str], allow_outside_tmpdir=False
+    ) -> List[Path]:
+        """Create the given set of files.
+
+        Unlike other helpers like :func:`makepyfile` this allows to specify
+        absolute paths, which need to be below :attr:`tmpdir` by default
+        (use `allow_outside_tmpdir` to write arbitrary files).
+        """
+        paths = []
+        if allow_outside_tmpdir:
+            validated_files = {Path(k): v for k, v in files.items()}
+        else:
+            tmpdir_path = Path(self.tmpdir)
+            validated_files = {
+                Path(k).absolute().relative_to(tmpdir_path): v for k, v in files.items()
+            }
+
+        for fpath, content in validated_files.items():
+            path = Path(self.tmpdir).joinpath(fpath)
+            with open(str(path), "w") as fp:
+                fp.write(textwrap.dedent(content))
+            paths.append(path)
+        return paths
+
     def syspathinsert(self, path=None):
         """Prepend a directory to sys.path, defaults to :py:attr:`tmpdir`.
 

testing/test_pytester.py

@@ -1,7 +1,9 @@
+import builtins
 import os
 import subprocess
 import sys
 import time
+from contextlib import contextmanager
 from typing import List
 
 import py.path
@@ -11,9 +13,11 @@
 from _pytest.config import PytestPluginManager
 from _pytest.main import ExitCode
 from _pytest.outcomes import Failed
+from _pytest.pathlib import Path
 from _pytest.pytester import CwdSnapshot
 from _pytest.pytester import HookRecorder
 from _pytest.pytester import LineMatcher
+from _pytest.pytester import MonkeyPatch
 from _pytest.pytester import SysModulesSnapshot
 from _pytest.pytester import SysPathsSnapshot
 from _pytest.pytester import Testdir
@@ -704,3 +708,45 @@ def test_error2(bad_fixture):
     result.assert_outcomes(error=2)
 
     assert result.parseoutcomes() == {"error": 2}
+
+
+def test_testdir_makefiles(testdir: Testdir, monkeypatch: MonkeyPatch) -> None:
+    tmpdir = testdir.tmpdir
+
+    abspath = str(tmpdir / "bar")
+
+    created_paths = testdir.makefiles({"foo": "", abspath: ""})
+    p1 = created_paths[0]
+    assert isinstance(p1, Path)
+    relpath = tmpdir / "foo"
+    assert p1 == relpath
+
+    p2 = created_paths[1]
+    assert p2.exists()
+    assert str(p2) == abspath
+
+    assert testdir.makefiles({}) == []
+
+    # Disallows creation outside of tmpdir by default.
+    with pytest.raises(
+        ValueError, match="'/abspath' does not start with '{}'".format(tmpdir)
+    ):
+        testdir.makefiles({"shouldnotbecreated": "", "/abspath": ""})
+    # Validation before creating anything.
+    assert not Path("shouldnotbecreated").exists()
+
+    # Support writing arbitrary files on request.
+    open_calls = []
+    orig_open = builtins.open
+
+    @contextmanager
+    def mocked_open(*args):
+        open_calls.append(["__enter__", args])
+        with orig_open(os.devnull, *args[1:]) as fp:
+            yield fp
+
+    with monkeypatch.context() as mp:
+        mp.setattr(builtins, "open", mocked_open)
+        created_paths = testdir.makefiles({"/abspath": ""}, allow_outside_tmpdir=True)
+    assert created_paths == [Path("/abspath")]
+    assert open_calls == [["__enter__", ("/abspath", "w")]]