diff --git a/.github/workflows/python-tests.yml b/.github/workflows/python-tests.yml
index 3cdea3eec0..8492e036b1 100644
--- a/.github/workflows/python-tests.yml
+++ b/.github/workflows/python-tests.yml
@@ -37,34 +37,20 @@ jobs:
           sudo apt-get update
           sudo apt-get install texlive-plain-generic inkscape texlive-xetex
           sudo apt-get install xvfb x11-utils libxkbcommon-x11-0 pandoc
-      - name: Run the tests
+      - name: Run the tests on posix
         if: ${{ !startsWith(matrix.python-version, 'pypy') && !startsWith(matrix.os, 'windows') }}
-        run: hatch run cov:test -W default || hatch run test:test -W default --lf
-      - name: Run the tests on pypy and windows
-        if: ${{ startsWith(matrix.python-version, 'pypy') || startsWith(matrix.os, 'windows') }}
-        run: hatch run test:test  -W default || hatch run test:test  -W default --lf
+        run: hatch run cov:test --cov-fail-under 75 || hatch run test:test --lf
+      - name: Run the tests on pypy
+        if: ${{ startsWith(matrix.python-version, 'pypy') }}
+        run: hatch run test:test || hatch run test:test --lf
+      - name: Run the tests on windows
+        if: ${{ startsWith(matrix.python-version, 'windows') }}
+        run: hatch run cov:nowarn -s || hatch run cov:nowarn --lf
       - name: Coverage
         run: |
           pip install codecov
           codecov
 
-  client8:
-    runs-on: ${{ matrix.os }}
-    timeout-minutes: 20
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: ["3.10"]
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-      - name: Base Setup
-        uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
-      - run: |
-          pip install -U pre jupyter_client
-          hatch run test:test || hatch run test:test  --lf
-
   pre-commit:
     name: pre-commit
     runs-on: ubuntu-latest
@@ -102,38 +88,30 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - name: Base Setup
-        uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
+      - uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
         with:
           python_version: "3.8"
-      - name: Install miniumum versions
-        uses: jupyterlab/maintainer-tools/.github/actions/install-minimums@v1
+      - uses: jupyterlab/maintainer-tools/.github/actions/install-minimums@v1
+        with:
+          only_create_file: 1
       - name: Run the unit tests
         run: |
-          pytest -vv -W default || pytest -vv -W default --lf
+          export PIP_CONSTRAINT="./contraints_file.txt"
+          hatch run test:nowarn || hatch run test:nowarn --lf
 
   test_prereleases:
     name: Test Prereleases
     runs-on: ubuntu-latest
     timeout-minutes: 20
     steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-      - name: Base Setup
-        uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
+      - uses: actions/checkout@v3
+      - uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
         with:
           python_version: "3.11"
-      - name: Install the Python dependencies
-        run: |
-          pip install --no-deps .
-          pip install --pre --upgrade ".[test]"
-      - name: List installed packages
-        run: |
-          pip freeze
-          pip check
       - name: Run the tests
         run: |
-          pytest -vv -W default || pytest -vv -W default --lf
+          export PIP_PRE=1
+          hatch run test:nowarn || hatch run test:nowarn --lf
 
   make_sdist:
     name: Make SDist
@@ -173,7 +151,6 @@ jobs:
       - test_docs
       - test_minimum_versions
       - test_prereleases
-      - client8
       - check_links
       - test_sdist
     runs-on: ubuntu-latest
diff --git a/jupyter_server/files/handlers.py b/jupyter_server/files/handlers.py
index de60117324..1c065ab38a 100644
--- a/jupyter_server/files/handlers.py
+++ b/jupyter_server/files/handlers.py
@@ -1,7 +1,6 @@
 """Serve files directly from the ContentsManager."""
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
-import json
 import mimetypes
 from base64 import decodebytes
 from typing import List
@@ -15,7 +14,7 @@
 AUTH_RESOURCE = "contents"
 
 
-class FilesHandler(JupyterHandler):
+class FilesHandler(JupyterHandler, web.StaticFileHandler):
     """serve files via ContentsManager
 
     Normally used when ContentsManager is not a FileContentsManager.
@@ -85,8 +84,6 @@ async def get(self, path, include_body=True):
             if model["format"] == "base64":
                 b64_bytes = model["content"].encode("ascii")
                 self.write(decodebytes(b64_bytes))
-            elif model["format"] == "json":
-                self.write(json.dumps(model["content"]))
             else:
                 self.write(model["content"])
             self.flush()
diff --git a/pyproject.toml b/pyproject.toml
index 5e286213aa..3b0e37242a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -104,7 +104,8 @@ dependencies = ["coverage", "pytest-cov"]
 [tool.hatch.envs.cov.env-vars]
 ARGS = "-vv --cov jupyter_server --cov-branch --cov-report term-missing:skip-covered"
 [tool.hatch.envs.cov.scripts]
-test = "python -m pytest $ARGS --cov-fail-under 75 {args}"
+test = "python -m pytest $ARGS {args}"
+nwarn = "python -m pytest $ARGS -W default {args}"
 integration = "python -m pytest $ARGS --integration_tests=true {args}"
 
 [tool.hatch.version]
diff --git a/tests/extension/test_serverextension.py b/tests/extension/test_serverextension.py
index 0953504c07..95f74eab80 100644
--- a/tests/extension/test_serverextension.py
+++ b/tests/extension/test_serverextension.py
@@ -11,6 +11,10 @@
 
 from jupyter_server.config_manager import BaseJSONConfigManager
 from jupyter_server.extension.serverextension import (
+    DisableServerExtensionApp,
+    ListServerExtensionsApp,
+    ServerExtensionApp,
+    ToggleServerExtensionApp,
     _get_config_dir,
     toggle_server_extension_python,
 )
@@ -112,3 +116,21 @@ def test_load_ordered(jp_serverapp, jp_server_config):
     assert jp_serverapp.mockII is True, "Mock II should have been loaded"
     assert jp_serverapp.mockI is True, "Mock I should have been loaded"
     assert jp_serverapp.mock_shared == "II", "Mock II should be loaded after Mock I"
+
+
+def test_server_extension_apps(jp_env_config_path, jp_extension_environ):
+    app = ToggleServerExtensionApp()
+    app.extra_args = "mock1"
+    app.start()
+
+    app = DisableServerExtensionApp()
+    app.extra_args = "mock1"
+    app.start()
+
+    app = ListServerExtensionsApp()
+    app.start()
+
+
+def test_server_extension_app():
+    app = ServerExtensionApp()
+    app.launch_instance(["list"])
diff --git a/tests/extension/test_utils.py b/tests/extension/test_utils.py
index 49a36b20ee..00849de267 100644
--- a/tests/extension/test_utils.py
+++ b/tests/extension/test_utils.py
@@ -1,6 +1,10 @@
+import logging
+import warnings
+
 import pytest
 
-from jupyter_server.extension.utils import validate_extension
+from jupyter_server.extension.utils import get_loader, get_metadata, validate_extension
+from tests.extension.mockextensions import mockext_sys
 
 # Use ServerApps environment because it monkeypatches
 # jupyter_core.paths and provides a config directory
@@ -17,3 +21,19 @@ def test_validate_extension():
     assert validate_extension("tests.extension.mockextensions.mockext_user")
     # enabled at Python
     assert validate_extension("tests.extension.mockextensions.mockext_py")
+
+
+def test_get_loader():
+    get_loader(mockext_sys)
+    with warnings.catch_warnings():
+        warnings.simplefilter("ignore")
+        assert get_loader(object()) is None
+
+
+def test_get_metadata():
+    _, ext_points = get_metadata("tests.extension.mockextensions.mockext_sys")
+    assert len(ext_points)
+    _, ext_points = get_metadata("tests", logger=logging.getLogger())
+    point = ext_points[0]
+    assert point["module"] == "tests"
+    assert point["name"] == "tests"
diff --git a/tests/test_files.py b/tests/test_files.py
index 06f1932591..8a93557577 100644
--- a/tests/test_files.py
+++ b/tests/test_files.py
@@ -10,6 +10,16 @@
 from .utils import expected_http_error
 
 
+@pytest.fixture(
+    params=[
+        "jupyter_server.files.handlers.FilesHandler",
+        "jupyter_server.base.handlers.AuthenticatedFileHandler",
+    ]
+)
+def jp_argv(request):
+    return ["--ContentsManager.files_handler_class=" + request.param]
+
+
 @pytest.fixture(
     params=[
         [False, ["å b"]],
@@ -33,6 +43,15 @@ async def fetch_expect_404(jp_fetch, *path_parts):
     assert expected_http_error(e, 404), [path_parts, e]
 
 
+async def test_file_types(jp_fetch, jp_root_dir):
+    path = Path(jp_root_dir, "test")
+    path.mkdir(parents=True, exist_ok=True)
+    foos = ["foo.tar.gz", "foo.bz", "foo.foo"]
+    for foo in foos:
+        (path / foo).write_text(foo)
+        await fetch_expect_200(jp_fetch, "test", foo)
+
+
 async def test_hidden_files(jp_fetch, jp_serverapp, jp_root_dir, maybe_hidden):
     is_hidden, path_parts = maybe_hidden
     path = Path(jp_root_dir, *path_parts)
@@ -85,7 +104,7 @@ async def test_contents_manager(jp_fetch, jp_serverapp, jp_root_dir):
 
     r = await jp_fetch("files/test.txt", method="GET")
     assert r.code == 200
-    assert r.headers["content-type"] == "text/plain; charset=UTF-8"
+    assert "text/plain" in r.headers["content-type"]
     assert r.body.decode() == "foobar"
 
 
diff --git a/tests/test_utils.py b/tests/test_utils.py
index d3e168ff60..53e3acbc05 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -2,6 +2,7 @@
 import socket
 import subprocess
 import sys
+import uuid
 import warnings
 from pathlib import Path
 from unittest.mock import patch
@@ -116,7 +117,9 @@ async def foo():
 @pytest.mark.skipif(os.name != "posix", reason="Requires unix sockets")
 def test_unix_socket_in_use(tmp_path):
     root_tmp_dir = Path("/tmp").resolve()
-    server_address = os.path.join(root_tmp_dir, os.path.basename(tmp_path))
+    server_address = os.path.join(root_tmp_dir, uuid.uuid4().hex)
+    if os.path.exists(server_address):
+        os.remove(server_address)
     sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
     sock.bind(server_address)
     sock.listen(0)