diff --git a/testing/conftest.py b/testing/conftest.py
index 4ea857a9..066df23a 100644
--- a/testing/conftest.py
+++ b/testing/conftest.py
@@ -1,7 +1,8 @@
-import pathlib
 import shutil
-import subprocess
 import sys
+from functools import lru_cache
+from typing import Callable
+from typing import Iterator
 
 import execnet
 import pytest
@@ -23,10 +24,15 @@ def pytest_runtest_setup(item):
 
 
 @pytest.fixture
-def makegateway(request):
+def group_function() -> Iterator[execnet.Group]:
     group = execnet.Group()
-    request.addfinalizer(lambda: group.terminate(0.5))
-    return group.makegateway
+    yield group
+    group.terminate(0.5)
+
+
+@pytest.fixture
+def makegateway(group_function) -> Callable[[str], execnet.gateway.Gateway]:
+    return group_function.makegateway
 
 
 pytest_plugins = ["pytester", "doctest"]
@@ -101,37 +107,16 @@ def pytest_generate_tests(metafunc):
         else:
             gwtypes = ["popen", "socket", "ssh", "proxy"]
         metafunc.parametrize("gw", gwtypes, indirect=True)
-    elif "anypython" in metafunc.fixturenames:
-        metafunc.parametrize(
-            "anypython",
-            indirect=True,
-            argvalues=("sys.executable", "pypy3"),
-        )
 
 
-def getexecutable(name, cache={}):
-    try:
-        return cache[name]
-    except KeyError:
-        if name == "sys.executable":
-            return pathlib.Path(sys.executable)
-        path = shutil.which(name)
-        executable = pathlib.Path(path) if path is not None else None
-        if executable:
-            if name == "jython":
-                popen = subprocess.Popen(
-                    [str(executable), "--version"],
-                    universal_newlines=True,
-                    stderr=subprocess.PIPE,
-                )
-                out, err = popen.communicate()
-                if not err or "2.5" not in err:
-                    executable = None
-        cache[name] = executable
-        return executable
+@lru_cache()
+def getexecutable(name):
+    if name == "sys.executable":
+        return sys.executable
+    return shutil.which(name)
 
 
-@pytest.fixture
+@pytest.fixture(params=("sys.executable", "pypy3"))
 def anypython(request):
     name = request.param
     executable = getexecutable(name)
diff --git a/testing/test_basics.py b/testing/test_basics.py
index 141f7d3f..5820c492 100644
--- a/testing/test_basics.py
+++ b/testing/test_basics.py
@@ -1,9 +1,14 @@
+from __future__ import annotations
+
 import inspect
 import os
 import subprocess
 import sys
 import textwrap
+from dataclasses import dataclass
 from io import BytesIO
+from pathlib import Path
+from typing import Any
 
 import execnet
 import pytest
@@ -21,9 +26,8 @@
 )
 
 
+@pytest.mark.parametrize("val", ["123", 42, [1, 2, 3], ["23", 25]])
 class TestSerializeAPI:
-    pytestmark = [pytest.mark.parametrize("val", ["123", 42, [1, 2, 3], ["23", 25]])]
-
     def test_serializer_api(self, val):
         dumped = execnet.dumps(val)
         val2 = execnet.loads(dumped)
@@ -31,9 +35,9 @@ def test_serializer_api(self, val):
 
     def test_mmap(self, tmp_path, val):
         mmap = pytest.importorskip("mmap").mmap
-        p = tmp_path / "data"
-        with p.open("wb") as f:
-            f.write(execnet.dumps(val))
+        p = tmp_path / "data.bin"
+
+        p.write_bytes(execnet.dumps(val))
         with p.open("r+b") as f:
             m = mmap(f.fileno(), 0)
             val2 = execnet.load(m)
@@ -112,67 +116,83 @@ def read_write_loop():
             break
 
 
-def test_io_message(anypython, tmp_path, execmodel):
-    check = tmp_path / "check.py"
-    check.write_text(
-        inspect.getsource(gateway_base)
-        + textwrap.dedent(
-            """
-        from io import BytesIO
-        import tempfile
-        temp_out = BytesIO()
-        temp_in = BytesIO()
-        io = Popen2IO(temp_out, temp_in, get_execmodel({backend!r}))
-        for i, handler in enumerate(Message._types):
-            print ("checking %s %s" %(i, handler))
-            for data in "hello", "hello".encode('ascii'):
-                msg1 = Message(i, i, dumps(data))
-                msg1.to_io(io)
-                x = io.outfile.getvalue()
-                io.outfile.truncate(0)
-                io.outfile.seek(0)
-                io.infile.seek(0)
-                io.infile.write(x)
-                io.infile.seek(0)
-                msg2 = Message.from_io(io)
-                assert msg1.channelid == msg2.channelid, (msg1, msg2)
-                assert msg1.data == msg2.data, (msg1.data, msg2.data)
-                assert msg1.msgcode == msg2.msgcode
-        print ("all passed")
-    """.format(
-                backend=execmodel.backend
-            ),
+IO_MESSAGE_EXTRA_SOURCE = """
+import sys
+backend = sys.argv[1]
+try:
+    from io import BytesIO
+except ImportError:
+    from StringIO import StringIO as BytesIO
+import tempfile
+temp_out = BytesIO()
+temp_in = BytesIO()
+io = Popen2IO(temp_out, temp_in, get_execmodel(backend))
+for i, handler in enumerate(Message._types):
+    print ("checking", i, handler)
+    for data in "hello", "hello".encode('ascii'):
+        msg1 = Message(i, i, dumps(data))
+        msg1.to_io(io)
+        x = io.outfile.getvalue()
+        io.outfile.truncate(0)
+        io.outfile.seek(0)
+        io.infile.seek(0)
+        io.infile.write(x)
+        io.infile.seek(0)
+        msg2 = Message.from_io(io)
+        assert msg1.channelid == msg2.channelid, (msg1, msg2)
+        assert msg1.data == msg2.data, (msg1.data, msg2.data)
+        assert msg1.msgcode == msg2.msgcode
+print ("all passed")
+"""
+
+
+@dataclass
+class Checker:
+    python: str
+    path: Path
+    idx: int = 0
+
+    def run_check(
+        self, script: str, *extra_args: str, **process_args: Any
+    ) -> subprocess.CompletedProcess[str]:
+        self.idx += 1
+        check_path = self.path / f"check{self.idx}.py"
+        check_path.write_text(script)
+        return subprocess.run(
+            [self.python, os.fspath(check_path), *extra_args],
+            capture_output=True,
+            text=True,
+            check=True,
+            **process_args,
         )
+
+
+@pytest.fixture
+def checker(anypython: str, tmp_path: Path) -> Checker:
+    return Checker(python=anypython, path=tmp_path)
+
+
+def test_io_message(checker, execmodel):
+    out = checker.run_check(
+        inspect.getsource(gateway_base) + IO_MESSAGE_EXTRA_SOURCE, execmodel.backend
     )
-    out = subprocess.run(
-        [str(anypython), str(check)], text=True, capture_output=True, check=True
-    ).stdout
-    print(out)
-    assert "all passed" in out
+    print(out.stdout)
+    assert "all passed" in out.stdout
 
 
-def test_popen_io(anypython, tmp_path, execmodel):
-    check = tmp_path / "check.py"
-    check.write_text(
+def test_popen_io(checker, execmodel):
+    out = checker.run_check(
         inspect.getsource(gateway_base)
-        + textwrap.dedent(
-            f"""
-        io = init_popen_io(get_execmodel({execmodel.backend!r}))
-        io.write("hello".encode('ascii'))
-        s = io.read(1)
-        assert s == "x".encode('ascii')
-    """
-        ),
+        + f"""
+io = init_popen_io(get_execmodel({execmodel.backend!r}))
+io.write(b"hello")
+s = io.read(1)
+assert s == b"x"
+""",
+        input="x",
     )
-    from subprocess import Popen, PIPE
-
-    args = [str(anypython), str(check)]
-    proc = Popen(args, stdin=PIPE, stdout=PIPE, stderr=PIPE)
-    proc.stdin.write(b"x")
-    stdout, stderr = proc.communicate()
-    print(stderr)
-    proc.wait()
-    assert b"hello" in stdout
+    print(out.stderr)
+    assert "hello" in out.stdout
 
 
 def test_popen_io_readloop(monkeypatch, execmodel):
@@ -190,60 +210,45 @@ def newread(numbytes):
     assert result == b"tes"
 
 
-def test_rinfo_source(anypython, tmp_path):
-    check = tmp_path / "check.py"
-    check.write_text(
-        textwrap.dedent(
-            """
-        class Channel:
-            def send(self, data):
-                assert eval(repr(data), {}) == data
-        channel = Channel()
-        """
-        )
-        + inspect.getsource(gateway.rinfo_source)
-        + textwrap.dedent(
-            """
-        print ('all passed')
-        """
-        )
+def test_rinfo_source(checker):
+    out = checker.run_check(
+        f"""
+class Channel:
+    def send(self, data):
+        assert eval(repr(data), {{}}) == data
+channel = Channel()
+{inspect.getsource(gateway.rinfo_source)}
+print ('all passed')
+"""
     )
-    out = subprocess.run(
-        [str(anypython), str(check)], text=True, capture_output=True, check=True
-    ).stdout
-    print(out)
-    assert "all passed" in out
 
+    print(out.stdout)
+    assert "all passed" in out.stdout
 
-def test_geterrortext(anypython, tmp_path):
-    check = tmp_path / "check.py"
-    check.write_text(
+
+def test_geterrortext(checker):
+    out = checker.run_check(
         inspect.getsource(gateway_base)
-        + textwrap.dedent(
-            """
-        class Arg:
-            pass
-        errortext = geterrortext((Arg, "1", 4))
-        assert "Arg" in errortext
-        import sys
-        try:
-            raise ValueError("17")
-        except ValueError:
-            excinfo = sys.exc_info()
-            s = geterrortext(excinfo)
-            assert "17" in s
-            print ("all passed")
+        + """
+class Arg:
+    pass
+errortext = geterrortext((Arg, "1", 4))
+assert "Arg" in errortext
+import sys
+try:
+    raise ValueError("17")
+except ValueError:
+    excinfo = sys.exc_info()
+    s = geterrortext(excinfo)
+    assert "17" in s
+    print ("all passed")
     """
-        )
     )
-    out = subprocess.run(
-        [str(anypython), str(check)], text=True, capture_output=True, check=True
-    ).stdout
-    print(out)
-    assert "all passed" in out
+    print(out.stdout)
+    assert "all passed" in out.stdout
 
 
-@pytest.mark.skipif(not hasattr(os, "dup"), reason="no os.dup")
+@pytest.mark.skipif("not hasattr(os, 'dup')")
 def test_stdouterrin_setnull(execmodel, capfd):
     gateway_base.init_popen_io(execmodel)
     os.write(1, b"hello")
@@ -297,15 +302,15 @@ def test_wire_protocol(self):
 class TestPureChannel:
     @pytest.fixture
     def fac(self, execmodel):
-        class Gateway:
+        class FakeGateway:
             def _trace(self, *args):
                 pass
 
             def _send(self, *k):
                 pass
 
-        Gateway.execmodel = execmodel
-        return ChannelFactory(Gateway())
+        FakeGateway.execmodel = execmodel
+        return ChannelFactory(FakeGateway())
 
     def test_factory_create(self, fac):
         chan1 = fac.new()
diff --git a/testing/test_rsync.py b/testing/test_rsync.py
index b8d39f86..fefd9a06 100644
--- a/testing/test_rsync.py
+++ b/testing/test_rsync.py
@@ -2,6 +2,7 @@
 import pathlib
 import platform
 import sys
+import types
 
 import execnet
 import pytest
@@ -36,19 +37,22 @@ def gw2(request, group):
 )
 
 
-@pytest.fixture
-def dirs(request, tmp_path):
-    t = tmp_path
+class _dirs(types.SimpleNamespace):
+    source: pathlib.Path
+    dest1: pathlib.Path
+    dest2: pathlib.Path
 
-    class dirs:
-        source = t / "source"
-        dest1 = t / "dest1"
-        dest2 = t / "dest2"
 
+@pytest.fixture
+def dirs(request, tmp_path) -> _dirs:
+    dirs = _dirs(
+        source=tmp_path / "source",
+        dest1=tmp_path / "dest1",
+        dest2=tmp_path / "dest2",
+    )
     dirs.source.mkdir()
     dirs.dest1.mkdir()
     dirs.dest2.mkdir()
-
     return dirs
 
 
diff --git a/testing/test_serializer.py b/testing/test_serializer.py
index f71486e7..621816b1 100644
--- a/testing/test_serializer.py
+++ b/testing/test_serializer.py
@@ -1,99 +1,69 @@
-import pathlib
-import shutil
+import os
 import subprocess
 import sys
-import tempfile
+from pathlib import Path
 
 import execnet
 import pytest
 
-MINOR_VERSIONS = {"3": "543210", "2": "76"}
 
-
-TEMPDIR = None
-_py3_wrapper = None
-
-
-def setup_module(mod):
-    mod.TEMPDIR = pathlib.Path(tempfile.mkdtemp())
-    mod._py3_wrapper = PythonWrapper(pathlib.Path(sys.executable))
-
-
-def teardown_module(mod):
-    shutil.rmtree(TEMPDIR)
-
-
-# we use the execnet folder in order to avoid triggering a missing apipkg
-pyimportdir = str(pathlib.Path(execnet.__file__).parent)
+# We use the execnet folder in order to avoid triggering a missing apipkg.
+pyimportdir = os.fspath(Path(execnet.__file__).parent)
 
 
 class PythonWrapper:
-    def __init__(self, executable):
+    def __init__(self, executable, tmp_path):
         self.executable = executable
+        self.tmp_path = tmp_path
 
-    def dump(self, obj_rep):
-        script_file = TEMPDIR.joinpath("dump.py")
+    def dump(self, obj_rep: str) -> bytes:
+        script_file = self.tmp_path.joinpath("dump.py")
         script_file.write_text(
-            """
+            f"""
 import sys
-sys.path.insert(0, %r)
+sys.path.insert(0, {pyimportdir!r})
 import gateway_base as serializer
-# Need binary output
 sys.stdout = sys.stdout.detach()
-sys.stdout.write(serializer.dumps_internal(%s))
+sys.stdout.write(serializer.dumps_internal({obj_rep}))
 """
-            % (pyimportdir, obj_rep)
         )
-        popen = subprocess.Popen(
-            [str(self.executable), str(script_file)],
-            stdin=subprocess.PIPE,
-            stderr=subprocess.PIPE,
-            stdout=subprocess.PIPE,
+        res = subprocess.run(
+            [str(self.executable), str(script_file)], capture_output=True, check=True
         )
-        stdout, stderr = popen.communicate()
-        ret = popen.returncode
-        if ret:
-            raise Exception(
-                "ExecutionFailed: %d  %s\n%s" % (ret, self.executable, stderr)
-            )
-        return stdout
-
-    def load(self, data, option_args="__class__"):
-        script_file = TEMPDIR.joinpath("load.py")
+        return res.stdout
+
+    def load(self, data: bytes):
+        script_file = self.tmp_path.joinpath("load.py")
         script_file.write_text(
-            r"""
+            rf"""
 import sys
-sys.path.insert(0, %r)
+sys.path.insert(0, {pyimportdir!r})
 import gateway_base as serializer
-sys.stdin = sys.stdin.detach()
-loader = serializer.Unserializer(sys.stdin)
-loader.%s
+from io import BytesIO
+data = {data!r}
+io = BytesIO(data)
+loader = serializer.Unserializer(io)
 obj = loader.load()
 sys.stdout.write(type(obj).__name__ + "\n")
-sys.stdout.write(repr(obj))"""
-            % (pyimportdir, option_args)
+sys.stdout.write(repr(obj))
+"""
         )
-        popen = subprocess.Popen(
-            [str(self.executable), str(script_file)],
-            stdin=subprocess.PIPE,
-            stderr=subprocess.PIPE,
-            stdout=subprocess.PIPE,
+        res = subprocess.run(
+            [self.executable, script_file],
+            capture_output=True,
         )
-        stdout, stderr = popen.communicate(data)
-        ret = popen.returncode
-        if ret:
-            raise Exception(
-                "ExecutionFailed: %d  %s\n%s" % (ret, self.executable, stderr)
-            )
-        return [s.decode("ascii") for s in stdout.splitlines()]
+        if res.returncode:
+            raise ValueError(res.stderr)
+
+        return res.stdout.decode("ascii").splitlines()
 
     def __repr__(self):
         return f"<PythonWrapper for {self.executable}>"
 
 
 @pytest.fixture
-def py3(request):
-    return _py3_wrapper
+def py3(request, tmp_path):
+    return PythonWrapper(sys.executable, tmp_path)
 
 
 @pytest.fixture
diff --git a/testing/test_termination.py b/testing/test_termination.py
index 0df29a76..282c1979 100644
--- a/testing/test_termination.py
+++ b/testing/test_termination.py
@@ -66,11 +66,8 @@ def test_termination_on_remote_channel_receive(monkeypatch, makegateway):
     gw.remote_exec("channel.receive()")
     gw._group.terminate()
     command = ["ps", "-p", str(pid)]
-    popen = subprocess.Popen(
-        command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True
-    )
-    out, err = popen.communicate()
-    assert str(pid) not in out, out
+    output = subprocess.run(command, capture_output=True, text=True)
+    assert str(pid) not in output.stdout, output
 
 
 def test_close_initiating_remote_no_error(testdir, anypython):
diff --git a/testing/test_threadpool.py b/testing/test_threadpool.py
index 75df627e..47a226d0 100644
--- a/testing/test_threadpool.py
+++ b/testing/test_threadpool.py
@@ -1,7 +1,6 @@
 import os
 import sys
 
-import py
 import pytest
 from execnet.gateway_base import WorkerPool