[tests] relocate core integration tests (#11146)

* relocate core integration tests

* add sys.path context manager

* cleanup

* try

* try2

* fix path

* doc

* style

* add dep

* add 2 more deps

src/transformers/testing_utils.py

@@ -24,6 +24,7 @@ import unittest
 from distutils.util import strtobool
 from io import StringIO
 from pathlib import Path
+from typing import Iterator, Union
 
 from .file_utils import (
     is_datasets_available,
@@ -621,6 +622,27 @@ class CaptureLogger:
         return f"captured: {self.out}\n"
 
 
+@contextlib.contextmanager
+# adapted from https://stackoverflow.com/a/64789046/9201239
+def ExtendSysPath(path: Union[str, os.PathLike]) -> Iterator[None]:
+    """
+    Temporary add given path to `sys.path`.
+
+    Usage ::
+
+       with ExtendSysPath('/path/to/dir'):
+           mymodule = importlib.import_module('mymodule')
+
+    """
+
+    path = os.fspath(path)
+    try:
+        sys.path.insert(0, path)
+        yield
+    finally:
+        sys.path.remove(path)
+
+
 class TestCasePlus(unittest.TestCase):
     """
     This class extends `unittest.TestCase` with additional features.