Recover datadir fixture needed for v3bwfile tests

tests/unit/conftest.py

@@ -27,6 +27,29 @@ class _PseudoArguments(argparse.Namespace):
             setattr(self, key, kw[key])
 
 
+@pytest.fixture()
+def datadir(request):
+    """ get, read, open test files from the "data" directory. """
+    class D:
+        def __init__(self, basepath):
+            self.basepath = basepath
+
+        def open(self, name, mode="r"):
+            return self.basepath.join(name).open(mode)
+
+        def join(self, name):
+            return self.basepath.join(name).strpath
+
+        def read(self, name):
+            with self.open(name, "r") as f:
+                return f.read()
+
+        def readlines(self, name):
+            with self.open(name, "r") as f:
+                return f.readlines()
+    return D(request.fspath.dirpath("data"))
+
+
 @pytest.fixture(scope='session')
 def parser():
     return create_parser()