Re-create the temp directory on resetting the filesystem (#818)

* Re-create the temp directory on resetting the filesystem

- the temp dir is now created during filesystem
  initialization instead of at patcher setup if configured
- this is only done by default if created from the Patcher
- fixes #814

* Call reset() from __init__

- change from review

5 files changed, 60 insertions, 27 deletions

diff --git a/CHANGES.md b/CHANGES.md
index 0f7a5de..cbbdc27 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,6 +1,12 @@
 # pyfakefs Release Notes
 The released versions correspond to PyPI releases.
 
+## Unreleased
+
+### Fixes
+* Re-create temp directory if it had been created before on resetting file system
+  (see [#814](../../issues/814)).
+
 ## [Version 5.2.2](https://pypi.python.org/pypi/pyfakefs/5.2.2) (2023-04-13)
 Fixes a regression in 5.2.0
 
diff --git a/pyfakefs/fake_filesystem.py b/pyfakefs/fake_filesystem.py
index 0b85e77..cacdb9c 100644
--- a/pyfakefs/fake_filesystem.py
+++ b/pyfakefs/fake_filesystem.py
@@ -85,6 +85,7 @@ import heapq
 import os
 import random
 import sys
+import tempfile
 from collections import namedtuple, OrderedDict
 from doctest import TestResults
 from enum import Enum
@@ -197,12 +198,17 @@ class FakeFilesystem:
         path_separator: str = os.path.sep,
         total_size: Optional[int] = None,
         patcher: Any = None,
+        create_temp_dir: bool = False,
     ) -> None:
         """
         Args:
             path_separator:  optional substitute for os.path.sep
             total_size: if not None, the total size in bytes of the
                 root filesystem.
+            patcher: the Patcher instance if created from the Patcher
+            create_temp_dir: If True, a temp directory is created on initialization.
+                Under Posix, if the temp directory is not `/tmp`, a link to the temp
+                path is additionally created at `/tmp`.
 
         Example usage to use the same path separator under all systems:
 
@@ -212,6 +218,7 @@ class FakeFilesystem:
         self.path_separator: str = path_separator
         self.alternative_path_separator: Optional[str] = os.path.altsep
         self.patcher = patcher
+        self.create_temp_dir = create_temp_dir
         if path_separator != os.sep:
             self.alternative_path_separator = None
 
@@ -228,7 +235,7 @@ class FakeFilesystem:
         # file systems on non-case-sensitive systems and vice verse
         self.is_case_sensitive: bool = not (self.is_windows_fs or self._is_macos)
 
-        self.root = FakeDirectory(self.path_separator, filesystem=self)
+        self.root: FakeDirectory
         self._cwd = ""
 
         # We can't query the current value without changing it:
@@ -244,9 +251,9 @@ class FakeFilesystem:
         self.last_ino: int = 0
         self.last_dev: int = 0
         self.mount_points: Dict[AnyString, Dict] = OrderedDict()
-        self._add_root_mount_point(total_size)
-        self._add_standard_streams()
-        self.dev_null: Any = FakeNullFile(self)
+        self.dev_null: Any = None
+        self.reset(total_size=total_size, init_pathlib=False)
+
         # set from outside if needed
         self.patch_open_code = PatchMode.OFF
         self.shuffle_listdir_results = False
@@ -330,21 +337,24 @@ class FakeFilesystem:
         self.reset()
         FakePathModule.reset(self)
 
-    def reset(self, total_size: Optional[int] = None):
+    def reset(self, total_size: Optional[int] = None, init_pathlib: bool = True):
         """Remove all file system contents and reset the root."""
         self.root = FakeDirectory(self.path_separator, filesystem=self)
 
         self.dev_null = FakeNullFile(self)
-        self.open_files = []
-        self._free_fd_heap = []
+        self.open_files.clear()
+        self._free_fd_heap.clear()
         self.last_ino = 0
         self.last_dev = 0
-        self.mount_points = OrderedDict()
+        self.mount_points.clear()
         self._add_root_mount_point(total_size)
         self._add_standard_streams()
-        from pyfakefs import fake_pathlib
+        if self.create_temp_dir:
+            self._create_temp_dir()
+        if init_pathlib:
+            from pyfakefs import fake_pathlib
 
-        fake_pathlib.init_module(self)
+            fake_pathlib.init_module(self)
 
     def _add_root_mount_point(self, total_size):
         mount_point = "C:" if self.is_windows_fs else self.path_separator
@@ -1380,7 +1390,7 @@ class FakeFilesystem:
         """
         if check_link and self.islink(file_path):
             return True
-        path = to_string(make_string_path(file_path))
+        path = to_string(self.make_string_path(file_path))
         if path is None:
             raise TypeError
         if not path:
@@ -2915,6 +2925,19 @@ class FakeFilesystem:
         self._add_open_file(StandardStreamWrapper(sys.stdout))
         self._add_open_file(StandardStreamWrapper(sys.stderr))
 
+    def _create_temp_dir(self):
+        # the temp directory is assumed to exist at least in `tempfile`,
+        # so we create it here for convenience
+        temp_dir = tempfile.gettempdir()
+        if not self.exists(temp_dir):
+            self.create_dir(temp_dir)
+        if sys.platform != "win32" and not self.exists("/tmp"):
+            # under Posix, we also create a link in /tmp if the path does not exist
+            self.create_symlink("/tmp", temp_dir)
+            # reset the used size to 0 to avoid having the link size counted
+            # which would make disk size tests more complicated
+            next(iter(self.mount_points.values()))["used_size"] = 0
+
 
 def _run_doctest() -> TestResults:
     import doctest
diff --git a/pyfakefs/fake_filesystem_unittest.py b/pyfakefs/fake_filesystem_unittest.py
index 00831b6..0e18055 100644
--- a/pyfakefs/fake_filesystem_unittest.py
+++ b/pyfakefs/fake_filesystem_unittest.py
@@ -35,7 +35,7 @@ Existing unit tests that use the real file system can be retrofitted to use
 pyfakefs by simply changing their base class from `:py:class`unittest.TestCase`
 to `:py:class`pyfakefs.fake_filesystem_unittest.TestCase`.
 """
-import _io  # type:ignore [import]
+import _io  # type:ignore[import]
 import doctest
 import functools
 import genericpath
@@ -844,7 +844,7 @@ class Patcher:
             self._stubs.smart_unset_all()
         self._stubs = mox3_stubout.StubOutForTesting()
 
-        self.fs = fake_filesystem.FakeFilesystem(patcher=self)
+        self.fs = fake_filesystem.FakeFilesystem(patcher=self, create_temp_dir=True)
         self.fs.patch_open_code = self.patch_open_code
         for name in self._fake_module_classes:
             self.fake_modules[name] = self._fake_module_classes[name](self.fs)
@@ -876,7 +876,6 @@ class Patcher:
         if self.has_fcopy_file:
             shutil._HAS_FCOPYFILE = False  # type: ignore[attr-defined]
 
-        temp_dir = tempfile.gettempdir()
         with warnings.catch_warnings():
             # ignore warnings, see #542 and #614
             warnings.filterwarnings("ignore")
@@ -891,17 +890,6 @@ class Patcher:
         linecache.open = self.original_open  # type: ignore[attr-defined]
         tokenize._builtin_open = self.original_open  # type: ignore
 
-        # the temp directory is assumed to exist at least in `tempfile`,
-        # so we create it here for convenience
-        assert self.fs is not None
-        self.fs.create_dir(temp_dir)
-        if sys.platform != "win32" and not self.fs.exists("/tmp"):
-            # under Posix, we also create a link in /tmp if the path does not exist
-            self.fs.create_symlink("/tmp", temp_dir)
-            # reset the used size to 0 to avoid having the link size counted
-            # which would make disk size tests more complicated
-            next(iter(self.fs.mount_points.values()))["used_size"] = 0
-
     def start_patching(self) -> None:
         if not self._patching:
             self._patching = True
diff --git a/pyfakefs/pytest_tests/pytest_plugin_test.py b/pyfakefs/pytest_tests/pytest_plugin_test.py
index 2222191..51f95cb 100644
--- a/pyfakefs/pytest_tests/pytest_plugin_test.py
+++ b/pyfakefs/pytest_tests/pytest_plugin_test.py
@@ -2,6 +2,7 @@
 import os
 import tempfile
 
+from pyfakefs.fake_filesystem import OSType
 from pyfakefs.fake_filesystem_unittest import Pause
 import pyfakefs.pytest_tests.io
 
@@ -60,3 +61,18 @@ def test_use_own_io_module(fs):
 
     stream = pyfakefs.pytest_tests.io.InputStream(filepath)
     assert stream.read() == "bar"
+
+
+def test_switch_to_windows(fs):
+    fs.os = OSType.WINDOWS
+    assert os.path.exists(tempfile.gettempdir())
+
+
+def test_switch_to_linux(fs):
+    fs.os = OSType.LINUX
+    assert os.path.exists(tempfile.gettempdir())
+
+
+def test_switch_to_macos(fs):
+    fs.os = OSType.MACOS
+    assert os.path.exists(tempfile.gettempdir())
diff --git a/pyfakefs/tests/fake_filesystem_unittest_test.py b/pyfakefs/tests/fake_filesystem_unittest_test.py
index f77677c..88b08d1 100644
--- a/pyfakefs/tests/fake_filesystem_unittest_test.py
+++ b/pyfakefs/tests/fake_filesystem_unittest_test.py
@@ -657,11 +657,11 @@ class TestTempDirCreation(fake_filesystem_unittest.TestCase):
     def setUp(self):
         self.setUpPyfakefs()
 
-    def testTempDirExists(self):
+    def test_tempdir_exists(self):
         self.assertTrue(os.path.exists(tempfile.gettempdir()))
 
     @unittest.skipIf(sys.platform == "win32", "POSIX only test")
-    def testTmpExists(self):
+    def test_tmp_exists(self):
         # directory or link under Linux, link under macOS
         self.assertTrue(os.path.exists("/tmp"))