[RFC] tests: make read_text() work with directories (#4155)

This PR is just a showcase to see how we like it. I've converted a few
tests to it, but there will be much more to come.

```
assert (tmp_dir / "file") == "contents"
assert (tmp_dir / "dir").read_text() == {"subdir": {"file": "hello"}}
```

This approach is nicer because it allows us to use a declaratory
asserts instead of relying on fs files. The problem becomes much more
apparent once you get into remote workspaces, where we `trees_equal`
doesn't work.

tests/dir_helpers.py

@@ -221,6 +221,17 @@ class TmpDir(pathlib.Path):
         finally:
             self.scm.checkout(old)
 
+    def read_text(self, *args, **kwargs):  # pylint: disable=signature-differs
+        # NOTE: on windows we'll get PermissionError instead of
+        # IsADirectoryError when we try to `open` a directory, so we can't
+        # rely on exception flow control
+        if self.is_dir():
+            return {
+                path.name: path.read_text(*args, **kwargs)
+                for path in self.iterdir()
+            }
+        return super().read_text(*args, **kwargs)
+
 
 def _coerce_filenames(filenames):
     if isinstance(filenames, (str, bytes, pathlib.PurePath)):

tests/func/test_get.py

@@ -10,7 +10,6 @@ from dvc.repo import Repo
 from dvc.repo.get import GetDVCFileError
 from dvc.system import System
 from dvc.utils.fs import makedirs
-from tests.utils import trees_equal
 
 
 def test_get_repo_file(tmp_dir, erepo_dir):
@@ -29,8 +28,7 @@ def test_get_repo_dir(tmp_dir, erepo_dir):
 
     Repo.get(os.fspath(erepo_dir), "dir", "dir_imported")
 
-    assert os.path.isdir("dir_imported")
-    trees_equal(erepo_dir / "dir", "dir_imported")
+    assert (tmp_dir / "dir_imported").read_text() == {"file": "contents"}
 
 
 @pytest.mark.parametrize(
@@ -44,7 +42,6 @@ def test_get_git_file(tmp_dir, erepo):
 
     Repo.get(os.fspath(erepo), src, dst)
 
-    assert (tmp_dir / dst).is_file()
     assert (tmp_dir / dst).read_text() == "hello"
 
 
@@ -61,8 +58,7 @@ def test_get_git_dir(tmp_dir, erepo):
 
     Repo.get(os.fspath(erepo), src, dst)
 
-    assert (tmp_dir / dst).is_dir()
-    trees_equal(erepo / src, tmp_dir / dst)
+    assert (tmp_dir / dst).read_text() == {"dir": {"file.txt": "hello"}}
 
 
 def test_cache_type_is_properly_overridden(tmp_dir, erepo_dir):

tests/func/test_import.py

@@ -11,7 +11,6 @@ from dvc.dvcfile import Dvcfile
 from dvc.exceptions import DownloadError, PathMissingError
 from dvc.system import System
 from dvc.utils.fs import makedirs, remove
-from tests.utils import trees_equal
 
 
 def test_import(tmp_dir, scm, dvc, erepo_dir):
@@ -73,8 +72,7 @@ def test_import_git_dir(tmp_dir, scm, dvc, git_dir, src_is_dvc):
 
     stage = dvc.imp(os.fspath(git_dir), "src", "dst")
 
-    assert (tmp_dir / "dst").is_dir()
-    trees_equal(git_dir / "src", tmp_dir / "dst")
+    assert (tmp_dir / "dst").read_text() == {"file.txt": "hello"}
     assert tmp_dir.scm.repo.git.check_ignore(os.fspath(tmp_dir / "dst"))
     assert stage.deps[0].def_repo == {
         "url": os.fspath(git_dir),
@@ -88,8 +86,7 @@ def test_import_dir(tmp_dir, scm, dvc, erepo_dir):
 
     stage = dvc.imp(os.fspath(erepo_dir), "dir", "dir_imported")
 
-    assert os.path.isdir("dir_imported")
-    trees_equal(erepo_dir / "dir", "dir_imported")
+    assert (tmp_dir / "dir_imported").read_text() == {"foo": "foo content"}
     assert scm.repo.git.check_ignore("dir_imported")
     assert stage.deps[0].def_repo == {
         "url": os.fspath(erepo_dir),
@@ -222,8 +219,7 @@ def test_pull_imported_directory_stage(tmp_dir, dvc, erepo_dir):
 
     dvc.pull(["dir_imported.dvc"])
 
-    assert os.path.isdir("dir_imported")
-    trees_equal(erepo_dir / "dir", "dir_imported")
+    assert (tmp_dir / "dir_imported").read_text() == {"foo": "foo content"}
 
 
 def test_download_error_pulling_imported_stage(tmp_dir, dvc, erepo_dir):

tests/utils/__init__.py

@@ -1,6 +1,5 @@
 import os
 from contextlib import contextmanager
-from filecmp import dircmp
 
 from dvc.scm import Git
 
@@ -20,15 +19,5 @@ def cd(newdir):
         os.chdir(prevdir)
 
 
-def trees_equal(dir_path_1, dir_path_2):
-
-    comparison = dircmp(dir_path_1, dir_path_2)
-
-    assert set(comparison.left_only) == set(comparison.right_only) == set()
-
-    for d in comparison.common_dirs:
-        trees_equal(os.path.join(dir_path_1, d), os.path.join(dir_path_2, d))
-
-
 def to_posixpath(path):
     return path.replace("\\", "/")