diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index aac1b7f..3c0992e 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -50,10 +50,11 @@ jobs:
         run: |
           python -m pip install -U pip
           python -m pip install -U setuptools wheel
-          python -m pip install -U coverage coveralls
+          python -m pip install -U coverage coveralls pytest
+          python -m pip install -e .
 
       - name: Run tests
-        run: coverage run testsuite.py
+        run: coverage run -m pytest
 
       - name: Check test coverage
         run: |
diff --git a/MANIFEST.in b/MANIFEST.in
index 9ab8716..b7fa563 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1,17 +1,14 @@
+include *.mk
 include *.rst
+include *.yml
+include LICENSE
 include Makefile
 include .coveragerc
 include .gitignore
 include tox.ini
-include testsuite.py
+include pytest.ini
+include conftest.py
 include tests.py
 include tests/*.txt
 include tests/sample-tree/snake.egg-info
 recursive-include tests/sample-tree *.py *.zip
-
-# added by check_manifest.py
-include *.yml
-include LICENSE
-
-# added by check_manifest.py
-include *.mk
diff --git a/README.rst b/README.rst
index 15e0b08..a25c987 100644
--- a/README.rst
+++ b/README.rst
@@ -28,7 +28,7 @@ Licence: MIT (https://mit-license.org/)
 
 |buildstatus|_ |appveyor|_ |coverage|_
 
-.. |buildstatus| image:: https://github.com/mgedmin/findimports/workflows/build/badge.svg?branch=master
+.. |buildstatus| image:: https://github.com/mgedmin/findimports/actions/workflows/build.yml/badge.svg?branch=master
 .. _buildstatus: https://github.com/mgedmin/findimports/actions
 
 .. |appveyor| image:: https://ci.appveyor.com/api/projects/status/github/mgedmin/findimports?branch=master&svg=true
diff --git a/appveyor.yml b/appveyor.yml
index 101b83f..5f3982a 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -24,8 +24,9 @@ install:
   - ps: if (-not (Test-Path $env:PYTHON)) { throw "No $env:PYTHON" }
   - "set PATH=%PYTHON%;%PYTHON%\\Scripts;%PATH%"
   - python --version
+  - pip install tox
 
 build: off
 
 test_script:
-  - python testsuite.py
+  - tox -e py
diff --git a/conftest.py b/conftest.py
new file mode 100644
index 0000000..17a6422
--- /dev/null
+++ b/conftest.py
@@ -0,0 +1,69 @@
+import linecache
+import os
+import pathlib
+import sys
+
+import pytest
+
+
+here = pathlib.Path(__file__).resolve().parent
+sample_tree = pathlib.Path(here, 'tests/sample-tree')
+
+
+class RedirectToStdout(object):
+    """A file-like object that prints to sys.stdout
+
+    A reason to use sys.stderr = RedirectToStdout() instead of assigning
+    sys.stderr = sys.stdout is when sys.stdout is later reassigned to a
+    different object (e.g. the StringIO that doctests use) and you want
+    sys.stderr to always refer to whatever sys.stdout is printing to.
+
+    Not all file methods are implemented, just the ones that were actually
+    needed.
+    """
+
+    def write(self, msg):
+        sys.stdout.write(msg)
+
+
+class RewriteBackslashes(object):
+    """A file-like object that normalizes path separators.
+
+    pytest doesn't allow custom doctest checkers, so I have to do terrible
+    crimes like this class.
+    """
+
+    def __init__(self):
+        self.real_stdout = sys.stdout
+
+    def write(self, msg):
+        self.real_stdout.write(msg.replace(os.path.sep, '/'))
+
+
+def create_tree(files):
+    f = None
+    try:
+        for line in files.splitlines():
+            if line.startswith('-- ') and line.endswith(' --'):
+                pathname = pathlib.Path(line.strip('- '))
+                pathname.parent.mkdir(parents=True, exist_ok=True)
+                if f is not None:
+                    f.close()
+                f = pathname.open('w')
+            elif f is not None:
+                print(line, file=f)
+    finally:
+        if f is not None:
+            f.close()
+
+
+@pytest.fixture(autouse=True)
+def doctest_setup(doctest_namespace, tmp_path, monkeypatch):
+    doctest_namespace['create_tree'] = create_tree
+    doctest_namespace['sample_tree'] = str(sample_tree)
+    monkeypatch.syspath_prepend(str(sample_tree.joinpath('zippedmodules.zip')))
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.setattr(sys, 'stderr', RedirectToStdout())
+    monkeypatch.setattr(sys, 'stdout', RewriteBackslashes())
+    yield
+    linecache.clearcache()
diff --git a/pytest.ini b/pytest.ini
new file mode 100644
index 0000000..b25e019
--- /dev/null
+++ b/pytest.ini
@@ -0,0 +1,3 @@
+[pytest]
+testpaths = tests.py tests/*.txt
+addopts = -ra -s
diff --git a/tests.py b/tests.py
index de925bc..8bfe7f3 100644
--- a/tests.py
+++ b/tests.py
@@ -1,15 +1,10 @@
 import os
 import unittest
+from io import StringIO
 
 import findimports
 
 
-try:
-    from cStringIO import StringIO
-except ImportError:
-    from io import StringIO
-
-
 here = os.path.dirname(__file__)
 
 
diff --git a/tests/cyclic-imports.txt b/tests/cyclic-imports.txt
index ccdd6fb..2ed5e8c 100644
--- a/tests/cyclic-imports.txt
+++ b/tests/cyclic-imports.txt
@@ -1,7 +1,5 @@
 Test cyclic imports
 
-    >>> from testsuite import create_tree
-
     >>> create_tree('''
     ... -- foo/__init__.py --
     ...
diff --git a/tests/import-statements.txt b/tests/import-statements.txt
index 81e6786..e2ddea5 100644
--- a/tests/import-statements.txt
+++ b/tests/import-statements.txt
@@ -8,10 +8,10 @@ All kinds of import statements are handled
     >>> with open('marmalade.py', 'w') as f: _ = f.write('''
     ... import sys
     ... import os.path
-    ... import email.Message as EM
+    ... import email.message as EM
     ... from . import foobar
-    ... from cStringIO import StringIO
-    ... from cPickle import dumps as D
+    ... from io import StringIO
+    ... from pickle import dumps as D
     ... from sys import (argv,
     ...                  exc_info as EI,  # complexity is fun
     ...                  exit)
@@ -23,10 +23,10 @@ All kinds of import statements are handled
     ...     print(imp)
     ImportInfo('sys', 'marmalade.py', 2, None)
     ImportInfo('os.path', 'marmalade.py', 3, None)
-    ImportInfo('email.Message', 'marmalade.py', 4, None)
+    ImportInfo('email.message', 'marmalade.py', 4, None)
     ImportInfo('foobar', 'marmalade.py', 5, 1)
-    ImportInfo('cStringIO.StringIO', 'marmalade.py', 6, 0)
-    ImportInfo('cPickle.dumps', 'marmalade.py', 7, 0)
+    ImportInfo('io.StringIO', 'marmalade.py', 6, 0)
+    ImportInfo('pickle.dumps', 'marmalade.py', 7, 0)
     ImportInfo('sys.argv', 'marmalade.py', 8, 0)
     ImportInfo('sys.exc_info', 'marmalade.py', 9, 0)
     ImportInfo('sys.exit', 'marmalade.py', 10, 0)
diff --git a/tests/package-graph.txt b/tests/package-graph.txt
index 9128575..66dc775 100644
--- a/tests/package-graph.txt
+++ b/tests/package-graph.txt
@@ -1,8 +1,6 @@
 Test collapsing to packages
 ===========================
 
-    >>> from testsuite import create_tree
-
     >>> create_tree('''
     ... -- foo/__init__.py --
     ...
diff --git a/tests/relative-imports.txt b/tests/relative-imports.txt
index e6726ac..7b63df9 100644
--- a/tests/relative-imports.txt
+++ b/tests/relative-imports.txt
@@ -1,8 +1,6 @@
 Test handling of relative imports
 =================================
 
-    >>> from testsuite import create_tree
-
     >>> create_tree('''
     ... -- foo/__init__.py --
     ...
diff --git a/tests/test-packages.txt b/tests/test-packages.txt
index a2bad2c..7c3a3e0 100644
--- a/tests/test-packages.txt
+++ b/tests/test-packages.txt
@@ -12,8 +12,6 @@ Test handling of test packages
     >>> g.removeTestPackage('tests')
     'tests'
 
-    >>> from testsuite import create_tree
-
     >>> create_tree('''
     ... -- foo/__init__.py --
     ...
diff --git a/tests/unknown-modules.txt b/tests/unknown-modules.txt
index 3ee0858..81232a4 100644
--- a/tests/unknown-modules.txt
+++ b/tests/unknown-modules.txt
@@ -8,7 +8,7 @@ We print warnings when we cannot find a module/package
     >>> with open('marmalade.py', 'w') as f: _ = f.write('''
     ... import sys
     ... import os.path
-    ... import email.Message as EM
+    ... import email.message as EM
     ... from . import foobar
     ... from io import StringIO
     ... from pickle import dumps as D
@@ -17,6 +17,7 @@ We print warnings when we cannot find a module/package
     ...                  exit)
     ... from email import *
     ... import imaginary.package
+    ... import curses.panel
     ... ''')
 
     >>> with open('foo.py', 'w') as f: _ = f.write('''
diff --git a/testsuite.py b/testsuite.py
deleted file mode 100755
index 474f2e4..0000000
--- a/testsuite.py
+++ /dev/null
@@ -1,96 +0,0 @@
-#!/usr/bin/python
-
-import doctest
-import glob
-import linecache
-import os
-import re
-import shutil
-import sys
-import tempfile
-import unittest
-
-
-class RedirectToStdout(object):
-    """A file-like object that prints to sys.stdout
-
-    A reason to use sys.stderr = RedirectToStdout() instead of assigning
-    sys.stderr = sys.stdout is when sys.stdout is later reassigned to a
-    different object (e.g. the StringIO that doctests use) and you want
-    sys.stderr to always refer to whatever sys.stdout is printing to.
-
-    Not all file methods are implemented, just the ones that were actually
-    needed.
-    """
-
-    def write(self, msg):
-        sys.stdout.write(msg)
-
-
-class Checker(doctest.OutputChecker):
-    """Doctest output checker for normalizing Windows pathname differences."""
-
-    def check_output(self, want, got, optionflags):
-        want = re.sub("sample-tree/[^:]*",
-                      lambda m: m.group(0).replace("/", os.path.sep),
-                      want)
-        return doctest.OutputChecker.check_output(self, want, got, optionflags)
-
-
-def setUp(test):
-    test.old_path = list(sys.path)
-    sample_tree = os.path.abspath(os.path.join('tests', 'sample-tree'))
-    sys.path.append(os.path.join(sample_tree, 'zippedmodules.zip'))
-    test.old_stderr = sys.stderr
-    sys.stderr = RedirectToStdout()
-    test.old_cwd = os.getcwd()
-    test.tempdir = tempfile.mkdtemp(prefix='test-findimports-')
-    os.chdir(test.tempdir)
-
-
-def tearDown(test):
-    sys.path[:] = test.old_path
-    sys.stderr = test.old_stderr
-    os.chdir(test.old_cwd)
-    shutil.rmtree(test.tempdir)
-    linecache.clearcache()
-
-
-def create_tree(files):
-    f = None
-    for line in files.splitlines():
-        if line.startswith('-- ') and line.endswith(' --'):
-            filename = line.strip('- ')
-            if not os.path.isdir(os.path.dirname(filename)):
-                os.makedirs(os.path.dirname(filename))
-            if f is not None:
-                f.close()
-            f = open(filename, 'w')
-        elif f is not None:
-            f.write(line + '\n')
-    if f is not None:
-        f.close()
-
-
-def additional_tests():  # hook for setuptools setup.py test
-    # paths relative to __file__ don't work if you run 'figleaf testsuite.py'
-    # so we have to use paths relative to os.getcwd()
-    sample_tree = os.path.abspath(os.path.join('tests', 'sample-tree'))
-    globs = dict(sample_tree=sample_tree)
-    doctests = sorted(glob.glob('tests/*.txt'))
-    return unittest.TestSuite([
-        unittest.defaultTestLoader.loadTestsFromName('tests'),
-        doctest.DocFileSuite(setUp=setUp, tearDown=tearDown,
-                             module_relative=False, globs=globs,
-                             checker=Checker(),
-                             optionflags=doctest.REPORT_NDIFF,
-                             *doctests),
-    ])
-
-
-def main():
-    unittest.main(defaultTest='additional_tests')
-
-
-if __name__ == '__main__':
-    main()
diff --git a/tox.ini b/tox.ini
index f06bbe4..2988ef8 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,30 +9,38 @@ envlist =
     py313
     pypy3
     flake8
+    ruff
     isort
     check-python-versions
 
 [testenv]
 deps =
+    pytest
 commands =
-    python testsuite.py {posargs}
+    pytest {posargs}
 
 [testenv:coverage]
 deps =
+    pytest
     coverage
 commands =
-    coverage run testsuite.py
+    coverage run -m pytest
     coverage report -m --fail-under=100
 
 [testenv:flake8]
 deps = flake8
 skip_install = true
-commands = flake8 findimports.py setup.py tests.py testsuite.py
+commands = flake8 findimports.py setup.py tests.py conftest.py
+
+[testenv:ruff]
+deps = ruff
+skip_install = true
+commands = ruff check findimports.py setup.py tests.py conftest.py
 
 [testenv:isort]
 deps = isort
 skip_install = true
-commands = isort {posargs: -c --diff findimports.py setup.py tests.py testsuite.py}
+commands = isort {posargs: -c --diff findimports.py setup.py tests.py conftest.py}
 
 [testenv:check-manifest]
 deps = check-manifest