GH-128520: Divide pathlib ABCs into three classes (#128523)

In the private pathlib ABCs, rename `PurePathBase` to `JoinablePath`, and
split `PathBase` into `ReadablePath` and `WritablePath`. This improves the
API fit for read-only virtual filesystems.

The split of `PathBase` entails a similar split of `CopyWorker` (implements
copying) and the test cases in `test_pathlib_abc`.

In a later patch, we'll make `WritablePath` inherit directly from
`JoinablePath` rather than `ReadablePath`. For a couple of reasons,
this isn't quite possible yet.

2 files changed, 243 insertions, 247 deletions

diff --git a/Lib/test/test_pathlib/test_pathlib.py b/Lib/test/test_pathlib/test_pathlib.py
index 6548577..ad5a9f9 100644
--- a/Lib/test/test_pathlib/test_pathlib.py
+++ b/Lib/test/test_pathlib/test_pathlib.py
@@ -75,7 +75,7 @@ class UnsupportedOperationTest(unittest.TestCase):
 # Tests for the pure classes.
 #
 
-class PurePathTest(test_pathlib_abc.DummyPurePathTest):
+class PurePathTest(test_pathlib_abc.DummyJoinablePathTest):
     cls = pathlib.PurePath
 
     # Make sure any symbolic links in the base test path are resolved.
@@ -924,7 +924,7 @@ class PurePathSubclassTest(PurePathTest):
 # Tests for the concrete classes.
 #
 
-class PathTest(test_pathlib_abc.DummyPathTest, PurePathTest):
+class PathTest(test_pathlib_abc.DummyWritablePathTest, PurePathTest):
     """Tests for the FS-accessing functionalities of the Path classes."""
     cls = pathlib.Path
     can_symlink = os_helper.can_symlink()
@@ -980,15 +980,15 @@ class PathTest(test_pathlib_abc.DummyPathTest, PurePathTest):
         self.addCleanup(os_helper.rmtree, d)
         return d
 
-    def test_matches_pathbase_docstrings(self):
-        path_names = {name for name in dir(pathlib._abc.PathBase) if name[0] != '_'}
+    def test_matches_writablepath_docstrings(self):
+        path_names = {name for name in dir(pathlib._abc.WritablePath) if name[0] != '_'}
         for attr_name in path_names:
             if attr_name == 'parser':
-                # On Windows, Path.parser is ntpath, but PathBase.parser is
+                # On Windows, Path.parser is ntpath, but WritablePath.parser is
                 # posixpath, and so their docstrings differ.
                 continue
             our_attr = getattr(self.cls, attr_name)
-            path_attr = getattr(pathlib._abc.PathBase, attr_name)
+            path_attr = getattr(pathlib._abc.WritablePath, attr_name)
             self.assertEqual(our_attr.__doc__, path_attr.__doc__)
 
     def test_concrete_class(self):
@@ -3019,7 +3019,7 @@ class PathTest(test_pathlib_abc.DummyPathTest, PurePathTest):
             P('c:/').group()
 
 
-class PathWalkTest(test_pathlib_abc.DummyPathWalkTest):
+class PathWalkTest(test_pathlib_abc.DummyReadablePathWalkTest):
     cls = pathlib.Path
     base = PathTest.base
     can_symlink = PathTest.can_symlink
diff --git a/Lib/test/test_pathlib/test_pathlib_abc.py b/Lib/test/test_pathlib/test_pathlib_abc.py
index 87aef0c..6ba012e 100644
--- a/Lib/test/test_pathlib/test_pathlib_abc.py
+++ b/Lib/test/test_pathlib/test_pathlib_abc.py
@@ -4,7 +4,7 @@ import os
 import errno
 import unittest
 
-from pathlib._abc import PurePathBase, PathBase
+from pathlib._abc import JoinablePath, ReadablePath, WritablePath
 from pathlib._types import Parser
 import posixpath
 
@@ -31,8 +31,8 @@ def needs_windows(fn):
 #
 
 
-class PurePathBaseTest(unittest.TestCase):
-    cls = PurePathBase
+class JoinablePathTest(unittest.TestCase):
+    cls = JoinablePath
 
     def test_magic_methods(self):
         P = self.cls
@@ -51,7 +51,7 @@ class PurePathBaseTest(unittest.TestCase):
         self.assertIs(self.cls.parser, posixpath)
 
 
-class DummyPurePath(PurePathBase):
+class DummyJoinablePath(JoinablePath):
     __slots__ = ('_segments',)
 
     def __init__(self, *segments):
@@ -63,7 +63,7 @@ class DummyPurePath(PurePathBase):
         return ''
 
     def __eq__(self, other):
-        if not isinstance(other, DummyPurePath):
+        if not isinstance(other, DummyJoinablePath):
             return NotImplemented
         return str(self) == str(other)
 
@@ -77,8 +77,8 @@ class DummyPurePath(PurePathBase):
         return type(self)(*pathsegments)
 
 
-class DummyPurePathTest(unittest.TestCase):
-    cls = DummyPurePath
+class DummyJoinablePathTest(unittest.TestCase):
+    cls = DummyJoinablePath
 
     # Use a base path that's unrelated to any real filesystem path.
     base = f'/this/path/kills/fascists/{TESTFN}'
@@ -916,9 +916,9 @@ class DummyPurePathTest(unittest.TestCase):
 #
 
 
-class DummyPathIO(io.BytesIO):
+class DummyWritablePathIO(io.BytesIO):
     """
-    Used by DummyPath to implement `open('w')`
+    Used by DummyWritablePath to implement `open('w')`
     """
 
     def __init__(self, files, path):
@@ -931,10 +931,10 @@ class DummyPathIO(io.BytesIO):
         super().close()
 
 
-class DummyPath(PathBase):
+class DummyReadablePath(ReadablePath):
     """
-    Simple implementation of PathBase that keeps files and directories in
-    memory.
+    Simple implementation of DummyReadablePath that keeps files and
+    directories in memory.
     """
     __slots__ = ('_segments')
 
@@ -950,7 +950,7 @@ class DummyPath(PathBase):
         return ''
 
     def __eq__(self, other):
-        if not isinstance(other, DummyPath):
+        if not isinstance(other, DummyReadablePath):
             return NotImplemented
         return str(self) == str(other)
 
@@ -990,10 +990,11 @@ class DummyPath(PathBase):
                 raise FileNotFoundError(errno.ENOENT, "File not found", path)
             stream = io.BytesIO(self._files[path])
         elif mode == 'w':
+            # FIXME: move to DummyWritablePath
             parent, name = posixpath.split(path)
             if parent not in self._directories:
                 raise FileNotFoundError(errno.ENOENT, "File not found", parent)
-            stream = DummyPathIO(self._files, path)
+            stream = DummyWritablePathIO(self._files, path)
             self._files[path] = b''
             self._directories[parent].add(name)
         else:
@@ -1011,6 +1012,10 @@ class DummyPath(PathBase):
         else:
             raise FileNotFoundError(errno.ENOENT, "File not found", path)
 
+
+class DummyWritablePath(DummyReadablePath, WritablePath):
+    __slots__ = ()
+
     def mkdir(self, mode=0o777, parents=False, exist_ok=False):
         path = str(self)
         parent = str(self.parent)
@@ -1029,24 +1034,11 @@ class DummyPath(PathBase):
             self.parent.mkdir(parents=True, exist_ok=True)
             self.mkdir(mode, parents=False, exist_ok=exist_ok)
 
-    def _delete(self):
-        path = str(self)
-        if path in self._files:
-            del self._files[path]
-        elif path in self._directories:
-            for name in list(self._directories[path]):
-                self.joinpath(name)._delete()
-            del self._directories[path]
-        else:
-            raise FileNotFoundError(errno.ENOENT, "File not found", path)
-        parent = str(self.parent)
-        self._directories[parent].remove(self.name)
-
 
-class DummyPathTest(DummyPurePathTest):
-    """Tests for PathBase methods that use stat(), open() and iterdir()."""
+class DummyReadablePathTest(DummyJoinablePathTest):
+    """Tests for ReadablePathTest methods that use stat(), open() and iterdir()."""
 
-    cls = DummyPath
+    cls = DummyReadablePath
     can_symlink = False
 
     # (self.base)
@@ -1138,213 +1130,6 @@ class DummyPathTest(DummyPurePathTest):
             self.assertIsInstance(f, io.BufferedIOBase)
             self.assertEqual(f.read().strip(), b"this is file A")
 
-    def test_read_write_bytes(self):
-        p = self.cls(self.base)
-        (p / 'fileA').write_bytes(b'abcdefg')
-        self.assertEqual((p / 'fileA').read_bytes(), b'abcdefg')
-        # Check that trying to write str does not truncate the file.
-        self.assertRaises(TypeError, (p / 'fileA').write_bytes, 'somestr')
-        self.assertEqual((p / 'fileA').read_bytes(), b'abcdefg')
-
-    def test_read_write_text(self):
-        p = self.cls(self.base)
-        (p / 'fileA').write_text('äbcdefg', encoding='latin-1')
-        self.assertEqual((p / 'fileA').read_text(
-            encoding='utf-8', errors='ignore'), 'bcdefg')
-        # Check that trying to write bytes does not truncate the file.
-        self.assertRaises(TypeError, (p / 'fileA').write_text, b'somebytes')
-        self.assertEqual((p / 'fileA').read_text(encoding='latin-1'), 'äbcdefg')
-
-    def test_read_text_with_newlines(self):
-        p = self.cls(self.base)
-        # Check that `\n` character change nothing
-        (p / 'fileA').write_bytes(b'abcde\r\nfghlk\n\rmnopq')
-        self.assertEqual((p / 'fileA').read_text(newline='\n'),
-                         'abcde\r\nfghlk\n\rmnopq')
-        # Check that `\r` character replaces `\n`
-        (p / 'fileA').write_bytes(b'abcde\r\nfghlk\n\rmnopq')
-        self.assertEqual((p / 'fileA').read_text(newline='\r'),
-                         'abcde\r\nfghlk\n\rmnopq')
-        # Check that `\r\n` character replaces `\n`
-        (p / 'fileA').write_bytes(b'abcde\r\nfghlk\n\rmnopq')
-        self.assertEqual((p / 'fileA').read_text(newline='\r\n'),
-                             'abcde\r\nfghlk\n\rmnopq')
-
-    def test_write_text_with_newlines(self):
-        p = self.cls(self.base)
-        # Check that `\n` character change nothing
-        (p / 'fileA').write_text('abcde\r\nfghlk\n\rmnopq', newline='\n')
-        self.assertEqual((p / 'fileA').read_bytes(),
-                         b'abcde\r\nfghlk\n\rmnopq')
-        # Check that `\r` character replaces `\n`
-        (p / 'fileA').write_text('abcde\r\nfghlk\n\rmnopq', newline='\r')
-        self.assertEqual((p / 'fileA').read_bytes(),
-                         b'abcde\r\rfghlk\r\rmnopq')
-        # Check that `\r\n` character replaces `\n`
-        (p / 'fileA').write_text('abcde\r\nfghlk\n\rmnopq', newline='\r\n')
-        self.assertEqual((p / 'fileA').read_bytes(),
-                         b'abcde\r\r\nfghlk\r\n\rmnopq')
-        # Check that no argument passed will change `\n` to `os.linesep`
-        os_linesep_byte = bytes(os.linesep, encoding='ascii')
-        (p / 'fileA').write_text('abcde\nfghlk\n\rmnopq')
-        self.assertEqual((p / 'fileA').read_bytes(),
-                          b'abcde' + os_linesep_byte + b'fghlk' + os_linesep_byte + b'\rmnopq')
-
-    def test_copy_file(self):
-        base = self.cls(self.base)
-        source = base / 'fileA'
-        target = base / 'copyA'
-        result = source.copy(target)
-        self.assertEqual(result, target)
-        self.assertTrue(target.exists())
-        self.assertEqual(source.read_text(), target.read_text())
-
-    def test_copy_file_to_existing_file(self):
-        base = self.cls(self.base)
-        source = base / 'fileA'
-        target = base / 'dirB' / 'fileB'
-        result = source.copy(target)
-        self.assertEqual(result, target)
-        self.assertTrue(target.exists())
-        self.assertEqual(source.read_text(), target.read_text())
-
-    def test_copy_file_to_existing_directory(self):
-        base = self.cls(self.base)
-        source = base / 'fileA'
-        target = base / 'dirA'
-        self.assertRaises(OSError, source.copy, target)
-
-    def test_copy_file_empty(self):
-        base = self.cls(self.base)
-        source = base / 'empty'
-        target = base / 'copyA'
-        source.write_bytes(b'')
-        result = source.copy(target)
-        self.assertEqual(result, target)
-        self.assertTrue(target.exists())
-        self.assertEqual(target.read_bytes(), b'')
-
-    def test_copy_file_to_itself(self):
-        base = self.cls(self.base)
-        source = base / 'empty'
-        source.write_bytes(b'')
-        self.assertRaises(OSError, source.copy, source)
-        self.assertRaises(OSError, source.copy, source, follow_symlinks=False)
-
-    def test_copy_dir_simple(self):
-        base = self.cls(self.base)
-        source = base / 'dirC'
-        target = base / 'copyC'
-        result = source.copy(target)
-        self.assertEqual(result, target)
-        self.assertTrue(target.is_dir())
-        self.assertTrue(target.joinpath('dirD').is_dir())
-        self.assertTrue(target.joinpath('dirD', 'fileD').is_file())
-        self.assertEqual(target.joinpath('dirD', 'fileD').read_text(),
-                         "this is file D\n")
-        self.assertTrue(target.joinpath('fileC').is_file())
-        self.assertTrue(target.joinpath('fileC').read_text(),
-                        "this is file C\n")
-
-    def test_copy_dir_complex(self, follow_symlinks=True):
-        def ordered_walk(path):
-            for dirpath, dirnames, filenames in path.walk(follow_symlinks=follow_symlinks):
-                dirnames.sort()
-                filenames.sort()
-                yield dirpath, dirnames, filenames
-        base = self.cls(self.base)
-        source = base / 'dirC'
-
-        if self.can_symlink:
-            # Add some symlinks
-            source.joinpath('linkC').symlink_to('fileC')
-            source.joinpath('linkD').symlink_to('dirD', target_is_directory=True)
-
-        # Perform the copy
-        target = base / 'copyC'
-        result = source.copy(target, follow_symlinks=follow_symlinks)
-        self.assertEqual(result, target)
-
-        # Compare the source and target trees
-        source_walk = ordered_walk(source)
-        target_walk = ordered_walk(target)
-        for source_item, target_item in zip(source_walk, target_walk, strict=True):
-            self.assertEqual(source_item[0].parts[len(source.parts):],
-                             target_item[0].parts[len(target.parts):])  # dirpath
-            self.assertEqual(source_item[1], target_item[1])  # dirnames
-            self.assertEqual(source_item[2], target_item[2])  # filenames
-            # Compare files and symlinks
-            for filename in source_item[2]:
-                source_file = source_item[0].joinpath(filename)
-                target_file = target_item[0].joinpath(filename)
-                if follow_symlinks or not source_file.is_symlink():
-                    # Regular file.
-                    self.assertEqual(source_file.read_bytes(), target_file.read_bytes())
-                elif source_file.is_dir():
-                    # Symlink to directory.
-                    self.assertTrue(target_file.is_dir())
-                    self.assertEqual(source_file.readlink(), target_file.readlink())
-                else:
-                    # Symlink to file.
-                    self.assertEqual(source_file.read_bytes(), target_file.read_bytes())
-                    self.assertEqual(source_file.readlink(), target_file.readlink())
-
-    def test_copy_dir_complex_follow_symlinks_false(self):
-        self.test_copy_dir_complex(follow_symlinks=False)
-
-    def test_copy_dir_to_existing_directory(self):
-        base = self.cls(self.base)
-        source = base / 'dirC'
-        target = base / 'copyC'
-        target.mkdir()
-        target.joinpath('dirD').mkdir()
-        self.assertRaises(FileExistsError, source.copy, target)
-
-    def test_copy_dir_to_existing_directory_dirs_exist_ok(self):
-        base = self.cls(self.base)
-        source = base / 'dirC'
-        target = base / 'copyC'
-        target.mkdir()
-        target.joinpath('dirD').mkdir()
-        result = source.copy(target, dirs_exist_ok=True)
-        self.assertEqual(result, target)
-        self.assertTrue(target.is_dir())
-        self.assertTrue(target.joinpath('dirD').is_dir())
-        self.assertTrue(target.joinpath('dirD', 'fileD').is_file())
-        self.assertEqual(target.joinpath('dirD', 'fileD').read_text(),
-                         "this is file D\n")
-        self.assertTrue(target.joinpath('fileC').is_file())
-        self.assertTrue(target.joinpath('fileC').read_text(),
-                        "this is file C\n")
-
-    def test_copy_dir_to_itself(self):
-        base = self.cls(self.base)
-        source = base / 'dirC'
-        self.assertRaises(OSError, source.copy, source)
-        self.assertRaises(OSError, source.copy, source, follow_symlinks=False)
-
-    def test_copy_dir_into_itself(self):
-        base = self.cls(self.base)
-        source = base / 'dirC'
-        target = base / 'dirC' / 'dirD' / 'copyC'
-        self.assertRaises(OSError, source.copy, target)
-        self.assertRaises(OSError, source.copy, target, follow_symlinks=False)
-        self.assertFalse(target.exists())
-
-    def test_copy_into(self):
-        base = self.cls(self.base)
-        source = base / 'fileA'
-        target_dir = base / 'dirA'
-        result = source.copy_into(target_dir)
-        self.assertEqual(result, target_dir / 'fileA')
-        self.assertTrue(result.exists())
-        self.assertEqual(source.read_text(), result.read_text())
-
-    def test_copy_into_empty_name(self):
-        source = self.cls('')
-        target_dir = self.base
-        self.assertRaises(ValueError, source.copy_into, target_dir)
-
     def test_iterdir(self):
         P = self.cls
         p = P(self.base)
@@ -1574,9 +1359,220 @@ class DummyPathTest(DummyPurePathTest):
             self.assertIs((P / 'linkA\x00').is_file(), False)
 
 
-class DummyPathWalkTest(unittest.TestCase):
-    cls = DummyPath
-    base = DummyPathTest.base
+class DummyWritablePathTest(DummyReadablePathTest):
+    cls = DummyWritablePath
+
+    def test_read_write_bytes(self):
+        p = self.cls(self.base)
+        (p / 'fileA').write_bytes(b'abcdefg')
+        self.assertEqual((p / 'fileA').read_bytes(), b'abcdefg')
+        # Check that trying to write str does not truncate the file.
+        self.assertRaises(TypeError, (p / 'fileA').write_bytes, 'somestr')
+        self.assertEqual((p / 'fileA').read_bytes(), b'abcdefg')
+
+    def test_read_write_text(self):
+        p = self.cls(self.base)
+        (p / 'fileA').write_text('äbcdefg', encoding='latin-1')
+        self.assertEqual((p / 'fileA').read_text(
+            encoding='utf-8', errors='ignore'), 'bcdefg')
+        # Check that trying to write bytes does not truncate the file.
+        self.assertRaises(TypeError, (p / 'fileA').write_text, b'somebytes')
+        self.assertEqual((p / 'fileA').read_text(encoding='latin-1'), 'äbcdefg')
+
+    def test_read_text_with_newlines(self):
+        p = self.cls(self.base)
+        # Check that `\n` character change nothing
+        (p / 'fileA').write_bytes(b'abcde\r\nfghlk\n\rmnopq')
+        self.assertEqual((p / 'fileA').read_text(newline='\n'),
+                         'abcde\r\nfghlk\n\rmnopq')
+        # Check that `\r` character replaces `\n`
+        (p / 'fileA').write_bytes(b'abcde\r\nfghlk\n\rmnopq')
+        self.assertEqual((p / 'fileA').read_text(newline='\r'),
+                         'abcde\r\nfghlk\n\rmnopq')
+        # Check that `\r\n` character replaces `\n`
+        (p / 'fileA').write_bytes(b'abcde\r\nfghlk\n\rmnopq')
+        self.assertEqual((p / 'fileA').read_text(newline='\r\n'),
+                             'abcde\r\nfghlk\n\rmnopq')
+
+    def test_write_text_with_newlines(self):
+        p = self.cls(self.base)
+        # Check that `\n` character change nothing
+        (p / 'fileA').write_text('abcde\r\nfghlk\n\rmnopq', newline='\n')
+        self.assertEqual((p / 'fileA').read_bytes(),
+                         b'abcde\r\nfghlk\n\rmnopq')
+        # Check that `\r` character replaces `\n`
+        (p / 'fileA').write_text('abcde\r\nfghlk\n\rmnopq', newline='\r')
+        self.assertEqual((p / 'fileA').read_bytes(),
+                         b'abcde\r\rfghlk\r\rmnopq')
+        # Check that `\r\n` character replaces `\n`
+        (p / 'fileA').write_text('abcde\r\nfghlk\n\rmnopq', newline='\r\n')
+        self.assertEqual((p / 'fileA').read_bytes(),
+                         b'abcde\r\r\nfghlk\r\n\rmnopq')
+        # Check that no argument passed will change `\n` to `os.linesep`
+        os_linesep_byte = bytes(os.linesep, encoding='ascii')
+        (p / 'fileA').write_text('abcde\nfghlk\n\rmnopq')
+        self.assertEqual((p / 'fileA').read_bytes(),
+                          b'abcde' + os_linesep_byte + b'fghlk' + os_linesep_byte + b'\rmnopq')
+
+    def test_copy_file(self):
+        base = self.cls(self.base)
+        source = base / 'fileA'
+        target = base / 'copyA'
+        result = source.copy(target)
+        self.assertEqual(result, target)
+        self.assertTrue(target.exists())
+        self.assertEqual(source.read_text(), target.read_text())
+
+    def test_copy_file_to_existing_file(self):
+        base = self.cls(self.base)
+        source = base / 'fileA'
+        target = base / 'dirB' / 'fileB'
+        result = source.copy(target)
+        self.assertEqual(result, target)
+        self.assertTrue(target.exists())
+        self.assertEqual(source.read_text(), target.read_text())
+
+    def test_copy_file_to_existing_directory(self):
+        base = self.cls(self.base)
+        source = base / 'fileA'
+        target = base / 'dirA'
+        self.assertRaises(OSError, source.copy, target)
+
+    def test_copy_file_empty(self):
+        base = self.cls(self.base)
+        source = base / 'empty'
+        target = base / 'copyA'
+        source.write_bytes(b'')
+        result = source.copy(target)
+        self.assertEqual(result, target)
+        self.assertTrue(target.exists())
+        self.assertEqual(target.read_bytes(), b'')
+
+    def test_copy_file_to_itself(self):
+        base = self.cls(self.base)
+        source = base / 'empty'
+        source.write_bytes(b'')
+        self.assertRaises(OSError, source.copy, source)
+        self.assertRaises(OSError, source.copy, source, follow_symlinks=False)
+
+    def test_copy_dir_simple(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        target = base / 'copyC'
+        result = source.copy(target)
+        self.assertEqual(result, target)
+        self.assertTrue(target.is_dir())
+        self.assertTrue(target.joinpath('dirD').is_dir())
+        self.assertTrue(target.joinpath('dirD', 'fileD').is_file())
+        self.assertEqual(target.joinpath('dirD', 'fileD').read_text(),
+                         "this is file D\n")
+        self.assertTrue(target.joinpath('fileC').is_file())
+        self.assertTrue(target.joinpath('fileC').read_text(),
+                        "this is file C\n")
+
+    def test_copy_dir_complex(self, follow_symlinks=True):
+        def ordered_walk(path):
+            for dirpath, dirnames, filenames in path.walk(follow_symlinks=follow_symlinks):
+                dirnames.sort()
+                filenames.sort()
+                yield dirpath, dirnames, filenames
+        base = self.cls(self.base)
+        source = base / 'dirC'
+
+        if self.can_symlink:
+            # Add some symlinks
+            source.joinpath('linkC').symlink_to('fileC')
+            source.joinpath('linkD').symlink_to('dirD', target_is_directory=True)
+
+        # Perform the copy
+        target = base / 'copyC'
+        result = source.copy(target, follow_symlinks=follow_symlinks)
+        self.assertEqual(result, target)
+
+        # Compare the source and target trees
+        source_walk = ordered_walk(source)
+        target_walk = ordered_walk(target)
+        for source_item, target_item in zip(source_walk, target_walk, strict=True):
+            self.assertEqual(source_item[0].parts[len(source.parts):],
+                             target_item[0].parts[len(target.parts):])  # dirpath
+            self.assertEqual(source_item[1], target_item[1])  # dirnames
+            self.assertEqual(source_item[2], target_item[2])  # filenames
+            # Compare files and symlinks
+            for filename in source_item[2]:
+                source_file = source_item[0].joinpath(filename)
+                target_file = target_item[0].joinpath(filename)
+                if follow_symlinks or not source_file.is_symlink():
+                    # Regular file.
+                    self.assertEqual(source_file.read_bytes(), target_file.read_bytes())
+                elif source_file.is_dir():
+                    # Symlink to directory.
+                    self.assertTrue(target_file.is_dir())
+                    self.assertEqual(source_file.readlink(), target_file.readlink())
+                else:
+                    # Symlink to file.
+                    self.assertEqual(source_file.read_bytes(), target_file.read_bytes())
+                    self.assertEqual(source_file.readlink(), target_file.readlink())
+
+    def test_copy_dir_complex_follow_symlinks_false(self):
+        self.test_copy_dir_complex(follow_symlinks=False)
+
+    def test_copy_dir_to_existing_directory(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        target = base / 'copyC'
+        target.mkdir()
+        target.joinpath('dirD').mkdir()
+        self.assertRaises(FileExistsError, source.copy, target)
+
+    def test_copy_dir_to_existing_directory_dirs_exist_ok(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        target = base / 'copyC'
+        target.mkdir()
+        target.joinpath('dirD').mkdir()
+        result = source.copy(target, dirs_exist_ok=True)
+        self.assertEqual(result, target)
+        self.assertTrue(target.is_dir())
+        self.assertTrue(target.joinpath('dirD').is_dir())
+        self.assertTrue(target.joinpath('dirD', 'fileD').is_file())
+        self.assertEqual(target.joinpath('dirD', 'fileD').read_text(),
+                         "this is file D\n")
+        self.assertTrue(target.joinpath('fileC').is_file())
+        self.assertTrue(target.joinpath('fileC').read_text(),
+                        "this is file C\n")
+
+    def test_copy_dir_to_itself(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        self.assertRaises(OSError, source.copy, source)
+        self.assertRaises(OSError, source.copy, source, follow_symlinks=False)
+
+    def test_copy_dir_into_itself(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        target = base / 'dirC' / 'dirD' / 'copyC'
+        self.assertRaises(OSError, source.copy, target)
+        self.assertRaises(OSError, source.copy, target, follow_symlinks=False)
+        self.assertFalse(target.exists())
+
+    def test_copy_into(self):
+        base = self.cls(self.base)
+        source = base / 'fileA'
+        target_dir = base / 'dirA'
+        result = source.copy_into(target_dir)
+        self.assertEqual(result, target_dir / 'fileA')
+        self.assertTrue(result.exists())
+        self.assertEqual(source.read_text(), result.read_text())
+
+    def test_copy_into_empty_name(self):
+        source = self.cls('')
+        target_dir = self.base
+        self.assertRaises(ValueError, source.copy_into, target_dir)
+
+
+class DummyReadablePathWalkTest(unittest.TestCase):
+    cls = DummyReadablePath
+    base = DummyReadablePathTest.base
     can_symlink = False
 
     def setUp(self):