diff --git a/src/ocrd/processor/base.py b/src/ocrd/processor/base.py
index 6107688bc..7c3d83e85 100644
--- a/src/ocrd/processor/base.py
+++ b/src/ocrd/processor/base.py
@@ -18,6 +18,7 @@
 import sys
 import tarfile
 import io
+from ocrd.workspace import Workspace
 
 from ocrd_utils import (
     VERSION as OCRD_VERSION,
@@ -49,7 +50,7 @@ class Processor():
 
     def __init__(
             self,
-            workspace,
+            workspace : Workspace,
             ocrd_tool=None,
             parameter=None,
             # TODO OCR-D/core#274
@@ -163,7 +164,7 @@ def verify(self):
         """
         return True
 
-    def process(self):
+    def process(self) -> None:
         """
         Process the :py:attr:`workspace` 
         from the given :py:attr:`input_file_grp`
diff --git a/src/ocrd/processor/builtin/dummy_processor.py b/src/ocrd/processor/builtin/dummy_processor.py
index 0fb00af53..774332a73 100644
--- a/src/ocrd/processor/builtin/dummy_processor.py
+++ b/src/ocrd/processor/builtin/dummy_processor.py
@@ -24,7 +24,7 @@ class DummyProcessor(Processor):
     Bare-bones processor creates PAGE-XML and optionally copies file from input group to output group
     """
 
-    def process(self):
+    def process(self) -> None:
         LOG = getLogger('ocrd.dummy')
         assert_file_grp_cardinality(self.input_file_grp, 1)
         assert_file_grp_cardinality(self.output_file_grp, 1)
diff --git a/src/ocrd/workspace.py b/src/ocrd/workspace.py
index 633e45acf..61c78c2e9 100644
--- a/src/ocrd/workspace.py
+++ b/src/ocrd/workspace.py
@@ -5,6 +5,7 @@
 from re import sub
 from tempfile import NamedTemporaryFile
 from contextlib import contextmanager
+from typing import Optional, Union
 
 from cv2 import COLOR_GRAY2BGR, COLOR_RGB2BGR, cvtColor
 from PIL import Image
@@ -13,6 +14,7 @@
 import requests
 
 from ocrd_models import OcrdMets, OcrdFile
+from ocrd_models.ocrd_file import ClientSideOcrdFile
 from ocrd_models.ocrd_page import parse, BorderType, to_xml
 from ocrd_modelfactory import exif_from_filename, page_from_file
 from ocrd_utils import (
@@ -71,7 +73,16 @@ class Workspace():
         baseurl (string) : Base URL to prefix to relative URL.
     """
 
-    def __init__(self, resolver, directory, mets=None, mets_basename=DEFAULT_METS_BASENAME, automatic_backup=False, baseurl=None, mets_server_url=None):
+    def __init__(
+        self,
+        resolver,
+        directory,
+        mets : Optional[Union[OcrdMets, ClientSideOcrdMets]] = None,
+        mets_basename=DEFAULT_METS_BASENAME,
+        automatic_backup=False,
+        baseurl=None,
+        mets_server_url=None
+    ):
         self.resolver = resolver
         self.directory = directory
         self.mets_target = str(Path(directory, mets_basename))
@@ -328,14 +339,16 @@ def rename_file_group(self, old, new):
             local_filename_replacements = {}
             log.info("Moving files")
             for mets_file in self.mets.find_files(fileGrp=old, local_only=True):
-                new_local_filename = old_local_filename = str(mets_file.local_filename)
+                new_local_filename = old_local_filename = mets_file.local_filename
+                assert new_local_filename
+                assert old_local_filename
                 # Directory part
                 new_local_filename = sub(r'^%s/' % old, r'%s/' % new, new_local_filename)
                 # File part
                 new_local_filename = sub(r'/%s' % old, r'/%s' % new, new_local_filename)
                 local_filename_replacements[str(mets_file.local_filename)] = new_local_filename
                 # move file from ``old`` to ``new``
-                mets_file.local_filename.rename(new_local_filename)
+                Path(old_local_filename).rename(new_local_filename)
                 # change the url of ``mets:file``
                 mets_file.local_filename = new_local_filename
                 # change the file ID and update structMap
@@ -375,7 +388,7 @@ def rename_file_group(self, old, new):
 
     @deprecated_alias(pageId="page_id")
     @deprecated_alias(ID="file_id")
-    def add_file(self, file_grp, content=None, **kwargs):
+    def add_file(self, file_grp, content=None, **kwargs) -> Union[OcrdFile, ClientSideOcrdFile]:
         """
         Add a file to the :py:class:`ocrd_models.ocrd_mets.OcrdMets` of the workspace.
 
diff --git a/src/ocrd_modelfactory/__init__.py b/src/ocrd_modelfactory/__init__.py
index e345ee061..7afc5b176 100644
--- a/src/ocrd_modelfactory/__init__.py
+++ b/src/ocrd_modelfactory/__init__.py
@@ -5,6 +5,7 @@
 """
 from datetime import datetime
 from pathlib import Path
+from typing import Tuple, Union
 from yaml import safe_load, safe_dump
 
 from PIL import Image
@@ -78,7 +79,7 @@ def page_from_image(input_file, with_tree=False):
     revmap = dict(((node, element) for element, node in mapping.items()))
     return pcgts, etree, mapping, revmap
 
-def page_from_file(input_file, with_tree=False):
+def page_from_file(input_file, with_tree=False) -> Union[PcGtsType, Tuple[PcGtsType, ET.Element, dict, dict]]:
     """
     Create :py:class:`~ocrd_models.ocrd_page.OcrdPage`
     from an :py:class:`~ocrd_models.ocrd_file.OcrdFile` or a file path
diff --git a/src/ocrd_models/ocrd_file.py b/src/ocrd_models/ocrd_file.py
index e8205a33d..963da2f96 100644
--- a/src/ocrd_models/ocrd_file.py
+++ b/src/ocrd_models/ocrd_file.py
@@ -1,13 +1,13 @@
 """
 API to ``mets:file``
 """
-from os.path import splitext, basename
 from pathlib import Path
+from typing import Any, List, Optional, Union
 
 from ocrd_utils import deprecation_warning
 
-from .ocrd_xml_base import ET
-from .constants import NAMESPACES as NS, TAG_METS_FLOCAT, TAG_METS_FILE
+from .ocrd_xml_base import ET # type: ignore
+from .constants import NAMESPACES as NS, TAG_METS_FLOCAT
 
 class OcrdFile():
     """
@@ -22,9 +22,8 @@ def __init__(self, el, mimetype=None, pageId=None, local_filename=None, mets=Non
             mets (OcrdMets): Containing :py:class:`ocrd_models.ocrd_mets.OcrdMets`.
             mimetype (string): ``@MIMETYPE`` of this ``mets:file``
             pageId (string): ``@ID`` of the physical ``mets:structMap`` entry corresponding to this ``mets:file``
-            local_filename (string): Local filename
             url (string): original ``@xlink:href`` of this ``mets:file``
-            local_filename (Path): ``@xlink:href`` pointing to the locally cached version of the file in the workspace
+            local_filename (string): ``@xlink:href`` pointing to the locally cached version of the file in the workspace
             ID (string): ``@ID`` of this ``mets:file``
             loctype (string): DEPRECATED do not use
         """
@@ -39,7 +38,7 @@ def __init__(self, el, mimetype=None, pageId=None, local_filename=None, mets=Non
         self.pageId = pageId
 
         if local_filename:
-            self.local_filename = Path(local_filename)
+            self.local_filename = local_filename
         if url:
             self.url = url
 
@@ -70,38 +69,38 @@ def __eq__(self, other):
                # self.fileGrp == other.fileGrp
 
     @property
-    def basename(self):
+    def basename(self) -> str:
         """
         Get the ``.name`` of the local file
         """
         if not self.local_filename:
-            return
-        return self.local_filename.name
+            return ''
+        return Path(self.local_filename).name
 
     @property
-    def extension(self):
+    def extension(self) -> str:
         if not self.local_filename:
-            return
-        return ''.join(self.local_filename.suffixes)
+            return ''
+        return ''.join(Path(self.local_filename).suffixes)
 
     @property
-    def basename_without_extension(self):
+    def basename_without_extension(self) -> str:
         """
         Get the ``os.path.basename`` of the local file, if any, with extension removed.
         """
         if not self.local_filename:
-            return
-        return self.local_filename.name[:-len(self.extension)]
+            return ''
+        return Path(self.local_filename).name[:-len(self.extension)]
 
     @property
-    def ID(self):
+    def ID(self) -> str:
         """
         Get the ``@ID`` of the ``mets:file``.
         """
         return self._el.get('ID')
 
     @ID.setter
-    def ID(self, ID):
+    def ID(self, ID : Optional[str]) -> None:
         """
         Set the ``@ID`` of the ``mets:file`` to :py:attr:`ID`.
         """
@@ -116,7 +115,7 @@ def ID(self, ID):
             self.pageId = pageId
 
     @property
-    def pageId(self):
+    def pageId(self) -> str:
         """
         Get the ``@ID`` of the physical ``mets:structMap`` entry corresponding to this ``mets:file`` (physical page manifestation).
         """
@@ -125,7 +124,7 @@ def pageId(self):
         return self.mets.get_physical_page_for_file(self)
 
     @pageId.setter
-    def pageId(self, pageId):
+    def pageId(self, pageId : Optional[str]) -> None:
         """
         Get the ``@ID`` of the physical ``mets:structMap`` entry corresponding to this ``mets:file`` (physical page manifestation) to :py:attr:`pageId`.
         """
@@ -136,21 +135,21 @@ def pageId(self, pageId):
         self.mets.set_physical_page_for_file(pageId, self)
 
     @property
-    def loctypes(self):
+    def loctypes(self) -> List[str]:
         """
         Get the ``@LOCTYPE``s of the ``mets:file``.
         """
         return [x.get('LOCTYPE') for x in  self._el.findall('mets:FLocat', NS)]
 
     @property
-    def mimetype(self):
+    def mimetype(self) -> str:
         """
         Get the ``@MIMETYPE`` of the ``mets:file``.
         """
         return self._el.get('MIMETYPE')
 
     @mimetype.setter
-    def mimetype(self, mimetype):
+    def mimetype(self, mimetype : Optional[str]) -> None:
         """
         Set the ``@MIMETYPE`` of the ``mets:file`` to :py:attr:`mimetype`.
         """
@@ -159,7 +158,7 @@ def mimetype(self, mimetype):
         self._el.set('MIMETYPE', mimetype)
 
     @property
-    def fileGrp(self):
+    def fileGrp(self) -> str:
         """
         The ``@USE`` of the containing ``mets:fileGrp``
         """
@@ -169,7 +168,7 @@ def fileGrp(self):
         raise ValueError("OcrdFile not related to METS")
 
     @property
-    def url(self):
+    def url(self) -> str:
         """
         Get the remote/original URL ``@xlink:href`` of this ``mets:file``.
         """
@@ -179,7 +178,7 @@ def url(self):
         return ''
 
     @url.setter
-    def url(self, url):
+    def url(self, url : Optional[str]) -> None:
         """
         Set the remote/original URL ``@xlink:href`` of this ``mets:file`` to :py:attr:`url`.
         """
@@ -194,16 +193,17 @@ def url(self, url):
         el_FLocat.set("LOCTYPE", "URL")
 
     @property
-    def local_filename(self):
+    def local_filename(self) -> Optional[str]:
         """
         Get the local/cached ``@xlink:href`` of this ``mets:file``.
         """
         el_FLocat = self._el.find('mets:FLocat[@LOCTYPE="OTHER"][@OTHERLOCTYPE="FILE"]', NS)
         if el_FLocat is not None:
-            return Path(el_FLocat.get("{%s}href" % NS["xlink"]))
+            return el_FLocat.get("{%s}href" % NS["xlink"])
+        return None
 
     @local_filename.setter
-    def local_filename(self, fname):
+    def local_filename(self, fname : Optional[Union[Path, str]]):
         """
         Set the local/cached ``@xlink:href`` of this ``mets:file`` to :py:attr:`local_filename`.
         """
@@ -212,9 +212,11 @@ def local_filename(self, fname):
             if el_FLocat is not None:
                 self._el.remove(el_FLocat)
             return
+        else:
+            fname = str(fname)
         if el_FLocat is None:
             el_FLocat = ET.SubElement(self._el, TAG_METS_FLOCAT)
-        el_FLocat.set("{%s}href" % NS["xlink"], str(fname))
+        el_FLocat.set("{%s}href" % NS["xlink"], fname)
         el_FLocat.set("LOCTYPE", "OTHER")
         el_FLocat.set("OTHERLOCTYPE", "FILE")
 
@@ -226,7 +228,18 @@ class ClientSideOcrdFile:
     this represents the response of the :py:class:`ocrd.mets_server.OcrdMetsServer`.
     """
 
-    def __init__(self, el, mimetype=None, pageId=None, loctype='OTHER', local_filename=None, mets=None, url=None, ID=None, fileGrp=None):
+    def __init__(
+        self,
+        el,
+        mimetype: str = '',
+        pageId: str = '',
+        loctype: str ='OTHER',
+        local_filename: Optional[str] = None,
+        mets : Any = None,
+        url: str = '',
+        ID: str = '',
+        fileGrp: str = ''
+    ):
         """
         Args:
             el (): ignored
diff --git a/src/ocrd_models/ocrd_mets.py b/src/ocrd_models/ocrd_mets.py
index ae4d75e29..19ccfb80e 100644
--- a/src/ocrd_models/ocrd_mets.py
+++ b/src/ocrd_models/ocrd_mets.py
@@ -4,7 +4,8 @@
 from datetime import datetime
 import re
 import typing
-from lxml import etree as ET
+from typing_extensions import Optional
+from lxml import etree as ET   # type: ignore
 from copy import deepcopy
 from warnings import warn
 
@@ -34,7 +35,7 @@
     METS_XML_EMPTY,
 )
 
-from .ocrd_xml_base import OcrdXmlDocument, ET
+from .ocrd_xml_base import OcrdXmlDocument
 from .ocrd_file import OcrdFile
 from .ocrd_agent import OcrdAgent
 
@@ -134,9 +135,9 @@ def _clear_caches(self):
         Deallocates the caches
         """
 
-        self._file_cache = None
-        self._page_cache = None
-        self._fptr_cache = None
+        self._file_cache = {}
+        self._page_cache = {}
+        self._fptr_cache = {}
         
     def refresh_caches(self):
         if self._cache_flag:
@@ -243,7 +244,7 @@ def find_files(
         pageId=None,
         mimetype=None,
         url=None,
-        local_filename=None,
+        local_filename : Optional[str] = None,
         local_only=False,
         include_fileGrp=None,
         exclude_fileGrp=None,
diff --git a/src/ocrd_models/ocrd_xml_base.py b/src/ocrd_models/ocrd_xml_base.py
index 7faefbad9..0617158b1 100644
--- a/src/ocrd_models/ocrd_xml_base.py
+++ b/src/ocrd_models/ocrd_xml_base.py
@@ -2,7 +2,7 @@
 Base class for XML documents loaded from either content or filename.
 """
 from os.path import exists
-from lxml import etree as ET
+from lxml import etree as ET   # type: ignore
 
 from .constants import NAMESPACES
 from .utils import xmllint_format
diff --git a/tests/cli/test_workspace.py b/tests/cli/test_workspace.py
index e96a39136..cf7eef3d0 100644
--- a/tests/cli/test_workspace.py
+++ b/tests/cli/test_workspace.py
@@ -461,7 +461,7 @@ def test_bulk_add0(self):
                 assert len(ws.mets.find_all_files(ID='//FILE_OCR-D-IMG_000.*')) == 10
                 assert len(ws.mets.find_all_files(ID='//FILE_.*_000.*')) == 20
                 assert len(ws.mets.find_all_files(pageId='PHYS_0001')) == 2
-                assert ws.mets.find_all_files(ID='FILE_OCR-D-PAGE_0001')[0].local_filename == Path('OCR-D-PAGE/FILE_0001.xml')
+                assert ws.mets.find_all_files(ID='FILE_OCR-D-PAGE_0001')[0].local_filename == 'OCR-D-PAGE/FILE_0001.xml'
 
     def test_bulk_add_missing_param(self):
         with pushd_popd(tempdir=True) as wsdir:
@@ -498,7 +498,7 @@ def test_bulk_add_gen_id(self):
             ws.reload_mets()
             print(out)
             assert next(ws.mets.find_files()).ID == 'b_c'
-            assert next(ws.mets.find_files()).local_filename == Path('d')
+            assert next(ws.mets.find_files()).local_filename == 'd'
             assert next(ws.mets.find_files()).url == 'https://host/b/d'
 
     def test_bulk_add_derive_local_filename(self):
@@ -517,7 +517,7 @@ def test_bulk_add_derive_local_filename(self):
             # print('out', out)
             # print('err', err)
             ws.reload_mets()
-            assert next(ws.mets.find_files()).local_filename == Path('srcdir/src.xml')
+            assert next(ws.mets.find_files()).local_filename == 'srcdir/src.xml'
 
     def test_bulk_add_stdin(self):
         resolver = Resolver()
@@ -550,7 +550,7 @@ def test_bulk_add_stdin(self):
                 f = next(ws.mets.find_files())
                 assert f.mimetype == 'image/png'
                 assert f.ID == 'FILE_0001_BIN.IMG-wolf'
-                assert f.local_filename == Path('BIN/FILE_0001_BIN.IMG-wolf.png')
+                assert f.local_filename == 'BIN/FILE_0001_BIN.IMG-wolf.png'
                 assert f.url == 'https://host/FILE_0001_BIN.IMG-wolf/BIN/FILE_0001_BIN.IMG-wolf.png'
 
     def test_list_page(self):
diff --git a/tests/model/test_ocrd_file.py b/tests/model/test_ocrd_file.py
index 98b9fa424..e057be784 100644
--- a/tests/model/test_ocrd_file.py
+++ b/tests/model/test_ocrd_file.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+from pathlib import Path
 import pytest
 
 from tests.base import (
@@ -61,7 +62,7 @@ def test_basename_from_url():
     Changed behavior, basename no longer derived from f.url
     """
     f = create_ocrd_file_with_defaults(url="http://foo.bar/quux")
-    assert f.basename == None
+    assert f.basename == ''
 
 
 @pytest.mark.parametrize("local_filename,extension",
@@ -74,6 +75,8 @@ def test_create_ocrd_file_with_defaults_extension(local_filename, extension):
 
     f = create_ocrd_file_with_defaults(local_filename=local_filename)
     assert f.extension == extension
+    assert not isinstance(f.local_filename, Path)
+    assert isinstance(f.local_filename, str)
 
 
 @pytest.mark.parametrize("local_filename,wo_extension",
diff --git a/tests/processor/test_ocrd_dummy.py b/tests/processor/test_ocrd_dummy.py
index 1f4ecc055..41b585c6b 100644
--- a/tests/processor/test_ocrd_dummy.py
+++ b/tests/processor/test_ocrd_dummy.py
@@ -3,7 +3,6 @@
 
 from io import BytesIO
 import os
-from pathlib import Path
 
 from PIL import Image
 
@@ -33,9 +32,8 @@ def test_copies_ok(self):
             )
             output_files = workspace.mets.find_all_files(fileGrp='OUTPUT')
             output_files.sort(key=lambda x: x.url)
-            print([str(s) for s in output_files])
-            assert output_files[0].local_filename == Path('OUTPUT/OUTPUT_PHYS_0001.tif')
-            assert output_files[1].local_filename == Path('OUTPUT/OUTPUT_PHYS_0001.xml')
+            assert output_files[0].local_filename == 'OUTPUT/OUTPUT_PHYS_0001.tif'
+            assert output_files[1].local_filename == 'OUTPUT/OUTPUT_PHYS_0001.xml'
             self.assertEqual(page_from_file(output_files[1]).pcGtsId, output_files[1].ID)
             assert page_from_file(output_files[1]).get_Page().imageFilename == str(output_files[0].local_filename)
             self.assertEqual(len(output_files), 6)
diff --git a/tests/test_mets_server.py b/tests/test_mets_server.py
index 59ee50e08..f61de4baf 100644
--- a/tests/test_mets_server.py
+++ b/tests/test_mets_server.py
@@ -1,3 +1,5 @@
+from collections.abc import Generator
+from typing import Iterable, Tuple
 from pytest import fixture, raises
 from tests.base import assets
 
@@ -22,7 +24,7 @@
 TRANSPORTS = ['/tmp/ocrd-mets-server.sock', 'http://127.0.0.1:12345']
 
 @fixture(scope='function', name='start_mets_server', params=TRANSPORTS)
-def fixture_start_mets_server(request):
+def fixture_start_mets_server(request) -> Iterable[Tuple[str, Workspace]]:
     def _start_mets_server(*args, **kwargs):
         mets_server = OcrdMetsServer(*args, **kwargs)
         mets_server.startup()
@@ -99,7 +101,6 @@ def test_mets_server_add_file(start_mets_server):
         'FOO'
     ])
     assert len(workspace_server.mets.find_all_files(fileGrp='FOO')) == NO_FILES
-    assert len(workspace_server.mets.find_all_files(file_grp='FOO')) == NO_FILES
 
     # not yet synced
     workspace_file = Workspace(Resolver(), WORKSPACE_DIR)
@@ -184,7 +185,7 @@ def test_mets_server_socket_stop(start_mets_server):
         # make sure the socket file was deleted on shutdown
         assert not Path(mets_server_url).exists()
 
-def test_find_all_files(start_mets_server):
+def test_find_all_files(start_mets_server : Tuple[str, Workspace]):
     _, workspace_server = start_mets_server
     assert len(workspace_server.mets.find_all_files()) == 35, '35 files total'
     assert len(workspace_server.mets.find_all_files(fileGrp='OCR-D-IMG')) == 3, '3 files in "OCR-D-IMG"'
@@ -203,7 +204,7 @@ def test_find_all_files(start_mets_server):
     assert len(workspace_server.mets.find_all_files(pageId='//PHYS_0001,//PHYS_0005')) == 18, '18 files in PHYS_001 and PHYS_0005 (two regexes)'
     assert len(workspace_server.mets.find_all_files(pageId='//PHYS_0005,PHYS_0001..PHYS_0002')) == 35, '35 files in //PHYS_0005,PHYS_0001..PHYS_0002'
 
-def test_reload(start_mets_server):
+def test_reload(start_mets_server : Tuple[str, Workspace]):
     _, workspace_server = start_mets_server
     workspace_server_copy = Workspace(Resolver(), workspace_server.directory)
     assert len(workspace_server.mets.find_all_files()) == 35, '35 files total'
diff --git a/tests/test_resolver.py b/tests/test_resolver.py
index bf9f4bb72..c162feb21 100644
--- a/tests/test_resolver.py
+++ b/tests/test_resolver.py
@@ -174,7 +174,7 @@ def test_workspace_from_url0():
 
     # assert
     assert '%s.tif' % f.ID == 'FILE_0001_IMAGE.tif'
-    assert f.local_filename == Path('OCR-D-IMG/FILE_0001_IMAGE.tif')
+    assert f.local_filename == 'OCR-D-IMG/FILE_0001_IMAGE.tif'
 
 
 def test_resolve_image0():
diff --git a/tests/test_workspace.py b/tests/test_workspace.py
index 18dd23331..df1818131 100644
--- a/tests/test_workspace.py
+++ b/tests/test_workspace.py
@@ -76,8 +76,8 @@ def test_workspace_add_file(plain_workspace):
     assert f.ID == 'ID1'
     assert f.mimetype == 'image/tiff'
     assert not f.url
-    assert f.local_filename == fpath
-    assert f.local_filename.exists()
+    assert f.local_filename == str(fpath)
+    assert Path(f.local_filename).exists()
 
 
 def test_workspace_add_file_overwrite(plain_workspace):
@@ -97,7 +97,7 @@ def test_workspace_add_file_overwrite(plain_workspace):
     assert f.ID == 'ID1'
     assert f.mimetype == 'image/tiff'
     assert not f.url
-    assert f.local_filename == fpath
+    assert f.local_filename == str(fpath)
     assert f.pageId == 'phys1'
     assert fpath.exists()
 
@@ -317,7 +317,7 @@ def test_rename_file_group(tmp_path):
     # act
     workspace.rename_file_group('OCR-D-IMG', 'FOOBAR')
     next_ocrd_file = next(workspace.mets.find_files(ID='OCR-D-GT-SEG-WORD_0001'))
-    next_ocrd_file.local_filename = tmp_path / relative_name
+    next_ocrd_file.local_filename = str(tmp_path / relative_name)
     pcgts_after = page_from_file(next_ocrd_file)
 
     # assert
@@ -358,12 +358,12 @@ def test_remove_file_group_flat(plain_workspace):
     """
 
     # act
-    added_res = plain_workspace.add_file('FOO', file_id='foo', mimetype='foo/bar', local_filename='file.ext', content='foo', page_id=None).url
+    added_res = plain_workspace.add_file('FOO', file_id='foo', mimetype='foo/bar', local_filename='file.ext', content='foo', page_id=None).local_filename
     # requires additional prepending of current path because not pushd_popd-magic at work
-    added_path = Path(join(plain_workspace.directory, added_res))
+    added_filename = join(plain_workspace.directory, added_res)
 
     # assert
-    assert added_path.exists()
+    assert Path(added_filename).exists()
     plain_workspace.remove_file_group('FOO', recursive=True)
 
 
@@ -408,8 +408,8 @@ def test_download_to_directory_from_workspace_download_file(plain_workspace):
     plain_workspace.download_file(f1)
     plain_workspace.download_file(f2)
 
-    assert f1.local_filename == Path('test.tif')
-    assert f2.local_filename == Path('test.xml')
+    assert f1.local_filename == 'test.tif'
+    assert f2.local_filename == 'test.xml'
 
 
 def test_save_image_file_invalid_mimetype_raises_exception(plain_workspace):
@@ -652,12 +652,12 @@ def test_merge_no_copy_files(tmp_path):
 
     ws1.merge(ws2, copy_files=False, fileId_mapping={'f1': 'f1_copy_files'})
 
-    assert next(ws1.mets.find_files(ID='f1_copy_files')).local_filename == Path('ws2/GRP2/f1')
+    assert next(ws1.mets.find_files(ID='f1_copy_files')).local_filename == 'ws2/GRP2/f1'
 
     with pytest.raises(FileExistsError):
         ws1.merge(ws2, copy_files=True, fileId_mapping={'f1': 'f1_copy_files'})
     ws1.merge(ws2, copy_files=True, fileId_mapping={'f1': 'f1_copy_files'}, force=True)
-    assert next(ws1.mets.find_files(ID='f1_copy_files')).local_filename == Path('GRP2/f1')
+    assert next(ws1.mets.find_files(ID='f1_copy_files')).local_filename == 'GRP2/f1'
 
 def test_merge_overwrite(tmp_path):
     # arrange