diff --git a/.azure-pipelines/syntax-validation.py b/.azure-pipelines/syntax-validation.py
index 6483683..9359ad8 100644
--- a/.azure-pipelines/syntax-validation.py
+++ b/.azure-pipelines/syntax-validation.py
@@ -12,7 +12,7 @@
             continue
         filename = os.path.normpath(os.path.join(base, f))
         try:
-            with open(filename, "r") as fh:
+            with open(filename) as fh:
                 ast.parse(fh.read())
         except SyntaxError as se:
             failures += 1
diff --git a/.azure-pipelines.yml b/.azure-pipelines.yml
index 288782f..2666f34 100644
--- a/.azure-pipelines.yml
+++ b/.azure-pipelines.yml
@@ -26,8 +26,6 @@
       vmImage: ubuntu-latest
     strategy:
       matrix:
-        python35:
-          PYTHON_VERSION: 3.5
         python36:
           PYTHON_VERSION: 3.6
         python37:
@@ -43,8 +41,6 @@
       vmImage: macOS-latest
     strategy:
       matrix:
-        python35:
-          PYTHON_VERSION: 3.5
         python36:
           PYTHON_VERSION: 3.6
         python37:
@@ -60,8 +56,6 @@
       vmImage: windows-latest
     strategy:
       matrix:
-        python35:
-          PYTHON_VERSION: 3.5
         python36:
           PYTHON_VERSION: 3.6
         python37:
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 853aac6..55f99c9 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -9,10 +9,3 @@
     directory: "/" # Location of package manifests
     schedule:
       interval: "monthly"
-    ignore:
-      - dependency-name: "mock"
-        # mock 4 requires Python 3.6+
-        versions: [">=4"]
-      - dependency-name: "twine"
-        # twine 2 requires Python 3.6+
-        versions: [">=2"]
diff --git a/.travis.yml b/.travis.yml
index 776ea00..523d7a0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,7 +12,6 @@
     - python: 3.8
     - python: 3.7
     - python: 3.6
-    - python: 3.5
     - os: osx
       language: generic
       env: CONDA=3.8 TOXENV=py38
@@ -22,9 +21,6 @@
     - os: osx
       language: generic
       env: CONDA=3.6 TOXENV=py36
-    - os: osx
-      language: generic
-      env: CONDA=3.5 TOXENV=py35
 
   allow_failures:
     - env: OPTIONAL=1
diff --git a/HISTORY.rst b/HISTORY.rst
index 73f9981..3c2b0d4 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -1,6 +1,10 @@
 =======
 History
 =======
+
+2.3.0 (????-??-??)
+------------------
+* Python 3.6+ only, support for Python 3.5 has been dropped
 
 2.2.0 (2020-09-07)
 ------------------
@@ -28,70 +32,58 @@
 
 2.0.0 (2020-06-24)
 ------------------
-
 * Python 3.5+ only, support for Python 2.7 has been dropped
 * Deprecated function alias run_process() has been removed
 * Fixed a stability issue on Windows
 
 1.1.0 (2019-11-04)
 ------------------
-
 * Add Python 3.8 support, drop Python 3.4 support
 
 1.0.2 (2019-05-20)
 ------------------
-
 * Stop environment override variables leaking into the process environment
 
 1.0.1 (2019-04-16)
 ------------------
-
 * Minor fixes on the return object (implement equality,
   mark as unhashable)
 
 1.0.0 (2019-03-25)
 ------------------
-
 * Support file system path objects (PEP-519) in arguments
 * Change the return object to make it similar to
   subprocess.CompletedProcess, introduced with Python 3.5+
 
 0.9.1 (2019-02-22)
 ------------------
-
 * Have deprecation warnings point to correct code locations
 
 0.9.0 (2018-12-07)
 ------------------
-
 * Trap UnicodeEncodeError when printing output. Offending characters
   are replaced and a warning is logged once. Hints at incorrectly set
   PYTHONIOENCODING.
 
 0.8.1 (2018-12-04)
 ------------------
-
 * Fix a few deprecation warnings
 
 0.8.0 (2018-10-09)
 ------------------
-
 * Add parameter working_directory to set the working directory
   of the subprocess
 
 0.7.2 (2018-10-05)
 ------------------
-
 * Officially support Python 3.7
 
 0.7.1 (2018-09-03)
 ------------------
-
 * Accept environment variable overriding with numeric values.
 
 0.7.0 (2018-05-13)
 ------------------
-
 * Unicode fixes. Fix crash on invalid UTF-8 input.
 * Clarify that stdout/stderr values are returned as bytestrings.
 * Callbacks receive the data decoded as UTF-8 unicode strings
@@ -101,23 +93,19 @@
 
 0.6.1 (2018-05-02)
 ------------------
-
 * Maintenance release to add some tests for executable resolution.
 
 0.6.0 (2018-05-02)
 ------------------
-
 * Fix Win32 API executable resolution for commands containing a dot ('.') in
   addition to a file extension (say '.bat').
 
 0.5.1 (2018-04-27)
 ------------------
-
 * Fix Win32API dependency installation on Windows.
 
 0.5.0 (2018-04-26)
 ------------------
-
 * New keyword 'win32resolve' which only takes effect on Windows and is enabled
   by default. This causes procrunner to call the Win32 API FindExecutable()
   function to try and lookup non-.exe files with the corresponding name. This
@@ -126,21 +114,17 @@
 
 0.4.0 (2018-04-23)
 ------------------
-
 * Python 2.7 support on Windows. Python3 not yet supported on Windows.
 
 0.3.0 (2018-04-17)
 ------------------
-
 * run_process() renamed to run()
 * Python3 compatibility fixes
 
 0.2.0 (2018-03-12)
 ------------------
-
 * Procrunner is now Python3 3.3-3.6 compatible.
 
 0.1.0 (2018-03-12)
 ------------------
-
 * First release on PyPI.
diff --git a/appveyor.yml b/appveyor.yml
index 9ae4a75..0cccda9 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -5,11 +5,9 @@
     # For Python versions available on Appveyor, see
     # http://www.appveyor.com/docs/installed-software#python
 
-    - PYTHON: "C:\\Python35"
     - PYTHON: "C:\\Python36"
     - PYTHON: "C:\\Python37"
     - PYTHON: "C:\\Python38"
-    - PYTHON: "C:\\Python35-x64"
     - PYTHON: "C:\\Python36-x64"
     - PYTHON: "C:\\Python37-x64"
     - PYTHON: "C:\\Python38-x64"
diff --git a/procrunner/__init__.py b/procrunner/__init__.py
index f5dd08e..1a8b176 100644
--- a/procrunner/__init__.py
+++ b/procrunner/__init__.py
@@ -275,7 +275,7 @@
     return obj
 
 
-def _windows_resolve(command):
+def _windows_resolve(command, path=None):
     """
     Try and find the full path and file extension of the executable to run.
     This is so that e.g. calls to 'somescript' will point at 'somescript.cmd'
@@ -290,7 +290,7 @@
     if not command or not isinstance(command[0], str):
         return command
 
-    found_executable = shutil.which(command[0])
+    found_executable = shutil.which(command[0], path=path)
     if found_executable:
         logger.debug("Resolved %s as %s", command[0], found_executable)
         return (found_executable, *command[1:])
@@ -299,7 +299,7 @@
         # Special case. shutil.which may not detect file extensions if a full
         # path is given, so try to resolve the executable explicitly
         for extension in os.getenv("PATHEXT").split(os.pathsep):
-            found_executable = shutil.which(command[0] + extension)
+            found_executable = shutil.which(command[0] + extension, path=path)
             if found_executable:
                 return (found_executable, *command[1:])
 
@@ -335,7 +335,7 @@
         if key in self._extras:
             return self._extras[key]
         if not hasattr(self, key):
-            raise KeyError("Unknown attribute {key}".format(key=key))
+            raise KeyError(f"Unknown attribute {key}")
         return getattr(self, key)
 
     def __eq__(self, other):
@@ -518,11 +518,13 @@
     command = tuple(_path_resolve(part) for part in command)
     if win32resolve and sys.platform == "win32":
         command = _windows_resolve(command)
+    if working_directory and sys.version_info < (3, 7):
+        working_directory = os.fspath(working_directory)
 
     p = subprocess.Popen(
         command,
         shell=False,
-        cwd=_path_resolve(working_directory),
+        cwd=working_directory,
         env=env,
         stdin=stdin_pipe,
         stdout=subprocess.PIPE,
diff --git a/requirements_dev.txt b/requirements_dev.txt
index 4d6c108..c25cd9e 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -1,7 +1,6 @@
 bump2version==1.0.0
 coverage==5.3
 flake8==3.8.3
-mock==3.0.5
 pip==20.2.3
 pytest==6.1.0
 Sphinx==3.2.1
diff --git a/setup.py b/setup.py
index 600e8c4..09c9259 100644
--- a/setup.py
+++ b/setup.py
@@ -13,7 +13,7 @@
 
 setup_requirements = []
 
-test_requirements = ["mock", "pytest"]
+test_requirements = ["pytest"]
 
 setup(
     author="Markus Gerstel",
@@ -25,7 +25,6 @@
         "Natural Language :: English",
         "Operating System :: OS Independent",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
@@ -40,7 +39,7 @@
     keywords="procrunner",
     name="procrunner",
     packages=find_packages(include=["procrunner"]),
-    python_requires=">=3.5",
+    python_requires=">=3.6",
     setup_requires=setup_requirements,
     test_suite="tests",
     tests_require=test_requirements,
diff --git a/tests/test_procrunner.py b/tests/test_procrunner.py
index b103183..8acec7c 100644
--- a/tests/test_procrunner.py
+++ b/tests/test_procrunner.py
@@ -1,6 +1,7 @@
 import copy
-import mock
+from unittest import mock
 import os
+import pathlib
 import procrunner
 import pytest
 import sys
@@ -86,13 +87,16 @@
         timeout=0.5,
         callback_stdout=mock.sentinel.callback_stdout,
         callback_stderr=mock.sentinel.callback_stderr,
-        working_directory=mock.sentinel.cwd,
+        working_directory=pathlib.Path("somecwd"),
         raise_timeout_exception=True,
     )
 
     assert mock_subprocess.Popen.called
     assert mock_subprocess.Popen.call_args[1]["env"] == os.environ
-    assert mock_subprocess.Popen.call_args[1]["cwd"] == mock.sentinel.cwd
+    assert mock_subprocess.Popen.call_args[1]["cwd"] in (
+        pathlib.Path("somecwd"),
+        "somecwd",
+    )
     mock_streamreader.assert_has_calls(
         [
             mock.call(
diff --git a/tests/test_procrunner_resolution.py b/tests/test_procrunner_resolution.py
index 2237c7c..e099be4 100644
--- a/tests/test_procrunner_resolution.py
+++ b/tests/test_procrunner_resolution.py
@@ -58,27 +58,25 @@
 
 
 @pytest.mark.skipif(sys.platform != "win32", reason="windows specific test only")
-def test_name_resolution_for_complex_cases(tmpdir):
-    tmpdir.chdir()
-
+def test_name_resolution_for_complex_cases(tmp_path):
     bat = "simple_bat_extension"
     cmd = "simple_cmd_extension"
     exe = "simple_exe_extension"
     dotshort = "more_complex_filename_with_a.dot"
     dotlong = "more_complex_filename.withadot"
 
-    (tmpdir / bat + ".bat").ensure()
-    (tmpdir / cmd + ".cmd").ensure()
-    (tmpdir / exe + ".exe").ensure()
-    (tmpdir / dotshort + ".bat").ensure()
-    (tmpdir / dotlong + ".cmd").ensure()
+    (tmp_path / (bat + ".bat")).touch()
+    (tmp_path / (cmd + ".cmd")).touch()
+    (tmp_path / (exe + ".exe")).touch()
+    (tmp_path / (dotshort + ".bat")).touch()
+    (tmp_path / (dotlong + ".cmd")).touch()
 
     def is_valid(command):
         assert len(command) == 1
-        assert os.path.exists(command[0])
+        assert os.path.exists(tmp_path / command[0])
 
-    is_valid(procrunner._windows_resolve([bat]))
-    is_valid(procrunner._windows_resolve([cmd]))
-    is_valid(procrunner._windows_resolve([exe]))
-    is_valid(procrunner._windows_resolve([dotshort]))
-    is_valid(procrunner._windows_resolve([dotlong]))
+    is_valid(procrunner._windows_resolve([bat], path=os.fspath(tmp_path)))
+    is_valid(procrunner._windows_resolve([cmd], path=os.fspath(tmp_path)))
+    is_valid(procrunner._windows_resolve([exe], path=os.fspath(tmp_path)))
+    is_valid(procrunner._windows_resolve([dotshort], path=os.fspath(tmp_path)))
+    is_valid(procrunner._windows_resolve([dotlong], path=os.fspath(tmp_path)))
diff --git a/tests/test_procrunner_system.py b/tests/test_procrunner_system.py
index eebc312..0dada84 100644
--- a/tests/test_procrunner_system.py
+++ b/tests/test_procrunner_system.py
@@ -40,11 +40,10 @@
     assert err == ""
 
 
-def test_running_wget(tmpdir):
-    tmpdir.chdir()
+def test_running_wget(tmp_path):
     command = ["wget", "https://www.google.com", "-O", "-"]
     try:
-        result = procrunner.run(command)
+        result = procrunner.run(command, working_directory=tmp_path)
     except OSError as e:
         if e.errno == 2:
             pytest.skip("wget not available")
@@ -54,15 +53,17 @@
     assert b"google" in result.stdout
 
 
-def test_path_object_resolution(tmpdir):
+def test_path_object_resolution(tmp_path):
     sentinel_value = b"sentinel"
-    tmpdir.join("tempfile").write(sentinel_value)
-    tmpdir.join("reader.py").write("with open('tempfile') as fh:\n    print(fh.read())")
+    tmp_path.joinpath("tempfile").write_bytes(sentinel_value)
+    tmp_path.joinpath("reader.py").write_text(
+        "with open('tempfile') as fh:\n    print(fh.read())"
+    )
     assert "LEAK_DETECTOR" not in os.environ
     result = procrunner.run(
-        [sys.executable, tmpdir.join("reader.py")],
+        [sys.executable, tmp_path / "reader.py"],
         environment_override={"PYTHONHASHSEED": "random", "LEAK_DETECTOR": "1"},
-        working_directory=tmpdir,
+        working_directory=tmp_path,
     )
     assert result.returncode == 0
     assert not result.stderr
diff --git a/tox.ini b/tox.ini
index b015248..fc76a2d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py35, py36, py37, py38, py39, flake8
+envlist = py36, py37, py38, py39, flake8
 
 [travis]
 python =
@@ -7,7 +7,6 @@
     3.8: py38
     3.7: py37
     3.6: py36
-    3.5: py35
 
 [testenv:azure]
 basepython = python