diff --git a/examples/simple/setup.py b/examples/simple/setup.py
index 9040c55e8..c15b12456 100755
--- a/examples/simple/setup.py
+++ b/examples/simple/setup.py
@@ -40,7 +40,7 @@ def add_data_files(path):
         'jinja2',
     ],
     extras_require = {
-        'test': ['pytest-jupyter'],
+        'test': ['pytest'],
     },
     include_package_data=True,
     cmdclass = cmdclass,
diff --git a/examples/simple/tests/conftest.py b/examples/simple/tests/conftest.py
new file mode 100644
index 000000000..87c6aff30
--- /dev/null
+++ b/examples/simple/tests/conftest.py
@@ -0,0 +1,3 @@
+pytest_plugins = [
+    'jupyter_server.pytest_plugin'
+]
diff --git a/jupyter_server/pytest_plugin.py b/jupyter_server/pytest_plugin.py
new file mode 100644
index 000000000..dee6d3f0d
--- /dev/null
+++ b/jupyter_server/pytest_plugin.py
@@ -0,0 +1,450 @@
+# Copyright (c) Jupyter Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+import os
+import sys
+import json
+import pytest
+import shutil
+import urllib.parse
+
+from binascii import hexlify
+
+import tornado
+from tornado.escape import url_escape
+import jupyter_core.paths
+import nbformat
+from traitlets.config import Config
+
+from jupyter_server.extension import serverextension
+from jupyter_server.serverapp import ServerApp
+from jupyter_server.utils import url_path_join
+from jupyter_server.services.contents.filemanager import FileContentsManager
+from jupyter_server.services.contents.largefilemanager import LargeFileManager
+
+
+# List of dependencies needed for this plugin.
+pytest_plugins = [
+    "pytest_tornasync",
+    # Once the chunk below moves to Jupyter Core, we'll uncomment
+    # This plugin and use the fixtures directly from Jupyter Core.
+    # "jupyter_core.pytest_plugin"
+]
+
+# ============ Move to Jupyter Core =============
+
+def mkdir(tmp_path, *parts):
+    path = tmp_path.joinpath(*parts)
+    if not path.exists():
+        path.mkdir(parents=True)
+    return path
+
+
+@pytest.fixture
+def jp_home_dir(tmp_path):
+    """Provides a temporary HOME directory value."""
+    return mkdir(tmp_path, "home")
+
+
+@pytest.fixture
+def jp_data_dir(tmp_path):
+    """Provides a temporary Jupyter data dir directory value."""
+    return mkdir(tmp_path, "data")
+
+
+@pytest.fixture
+def jp_config_dir(tmp_path):
+    """Provides a temporary Jupyter config dir directory value."""
+    return mkdir(tmp_path, "config")
+
+
+@pytest.fixture
+def jp_runtime_dir(tmp_path):
+    """Provides a temporary Jupyter runtime dir directory value."""
+    return mkdir(tmp_path, "runtime")
+
+
+@pytest.fixture
+def jp_system_jupyter_path(tmp_path):
+    """Provides a temporary Jupyter system path value."""
+    return mkdir(tmp_path, "share", "jupyter")
+
+
+@pytest.fixture
+def jp_env_jupyter_path(tmp_path):
+    """Provides a temporary Jupyter env system path value."""
+    return mkdir(tmp_path, "env", "share", "jupyter")
+
+
+@pytest.fixture
+def jp_system_config_path(tmp_path):
+    """Provides a temporary Jupyter config path value."""
+    return mkdir(tmp_path, "etc", "jupyter")
+
+
+@pytest.fixture
+def jp_env_config_path(tmp_path):
+    """Provides a temporary Jupyter env config path value."""
+    return mkdir(tmp_path, "env", "etc", "jupyter")
+
+
+@pytest.fixture
+def jp_environ(
+    monkeypatch,
+    tmp_path,
+    jp_home_dir,
+    jp_data_dir,
+    jp_config_dir,
+    jp_runtime_dir,
+    jp_system_jupyter_path,
+    jp_system_config_path,
+    jp_env_jupyter_path,
+    jp_env_config_path,
+):
+    """Configures a temporary environment based on Jupyter-specific environment variables. """
+    monkeypatch.setenv("HOME", str(jp_home_dir))
+    monkeypatch.setenv("PYTHONPATH", os.pathsep.join(sys.path))
+    # monkeypatch.setenv("JUPYTER_NO_CONFIG", "1")
+    monkeypatch.setenv("JUPYTER_CONFIG_DIR", str(jp_config_dir))
+    monkeypatch.setenv("JUPYTER_DATA_DIR", str(jp_data_dir))
+    monkeypatch.setenv("JUPYTER_RUNTIME_DIR", str(jp_runtime_dir))
+    monkeypatch.setattr(
+        jupyter_core.paths, "SYSTEM_JUPYTER_PATH", [str(jp_system_jupyter_path)]
+    )
+    monkeypatch.setattr(jupyter_core.paths, "ENV_JUPYTER_PATH", [str(jp_env_jupyter_path)])
+    monkeypatch.setattr(
+        jupyter_core.paths, "SYSTEM_CONFIG_PATH", [str(jp_system_config_path)]
+    )
+    monkeypatch.setattr(jupyter_core.paths, "ENV_CONFIG_PATH", [str(jp_env_config_path)])
+
+
+# ================= End: Move to Jupyter core ================
+
+# NOTE: This is a temporary fix for Windows 3.8
+# We have to override the io_loop fixture with an
+# asyncio patch. This will probably be removed in
+# the future.
+@pytest.fixture
+def jp_asyncio_patch():
+    """Appropriately configures the event loop policy if running on Windows w/ Python >= 3.8."""
+    ServerApp()._init_asyncio_patch()
+
+
+@pytest.fixture
+def io_loop(jp_asyncio_patch):
+    """Returns an ioloop instance that includes the asyncio patch for Windows 3.8 platforms."""
+    loop = tornado.ioloop.IOLoop()
+    loop.make_current()
+    yield loop
+    loop.clear_current()
+    loop.close(all_fds=True)
+
+
+@pytest.fixture
+def jp_server_config():
+    """Allows tests to setup their specific configuration values. """
+    return {}
+
+
+@pytest.fixture
+def jp_root_dir(tmp_path):
+    """Provides a temporary Jupyter root directory value."""
+    return mkdir(tmp_path, "root_dir")
+
+
+@pytest.fixture
+def jp_template_dir(tmp_path):
+    """Provides a temporary Jupyter templates directory value."""
+    return mkdir(tmp_path, "templates")
+
+
+@pytest.fixture
+def jp_argv():
+    """Allows tests to setup specific argv values. """
+    return []
+
+
+@pytest.fixture
+def jp_extension_environ(jp_env_config_path, monkeypatch):
+    """Monkeypatch a Jupyter Extension's config path into each test's environment variable"""
+    monkeypatch.setattr(serverextension, "ENV_CONFIG_PATH", [str(jp_env_config_path)])
+
+
+@pytest.fixture
+def jp_http_port(http_server_port):
+    """Returns the port value from the http_server_port fixture. """
+    return http_server_port[-1]
+
+
+@pytest.fixture
+def jp_nbconvert_templates(jp_data_dir):
+    """Setups up a temporary directory consisting of the nbconvert templates."""
+
+    # Get path to nbconvert template directory *before*
+    # monkeypatching the paths env variable via the jp_environ fixture.
+    possible_paths = jupyter_core.paths.jupyter_path('nbconvert', 'templates')
+    nbconvert_path = None
+    for path in possible_paths:
+        if os.path.exists(path):
+            nbconvert_path = path
+            break
+
+    nbconvert_target = jp_data_dir / 'nbconvert' / 'templates'
+
+    # copy nbconvert templates to new tmp data_dir.
+    if nbconvert_path:
+        shutil.copytree(nbconvert_path, str(nbconvert_target))
+
+
+@pytest.fixture(scope='function')
+def jp_configurable_serverapp(
+    jp_nbconvert_templates,  # this fixture must preceed jp_environ
+    jp_environ,
+    jp_server_config,
+    jp_argv,
+    jp_http_port,
+    jp_base_url,
+    tmp_path,
+    jp_root_dir,
+    io_loop,
+):
+    """Starts a Jupyter Server instance based on
+    the provided configuration values.
+
+    The fixture is a factory; it can be called like
+    a function inside a unit test. Here's a basic
+    example of how use this fixture:
+
+    .. code-block:: python
+
+        def my_test(jp_configurable_serverapp):
+
+            app = jp_configurable_serverapp(...)
+            ...
+    """
+    ServerApp.clear_instance()
+
+    def _configurable_serverapp(
+        config=jp_server_config,
+        base_url=jp_base_url,
+        argv=jp_argv,
+        environ=jp_environ,
+        http_port=jp_http_port,
+        tmp_path=tmp_path,
+        root_dir=jp_root_dir,
+        **kwargs
+    ):
+        c = Config(config)
+        c.NotebookNotary.db_file = ":memory:"
+        token = hexlify(os.urandom(4)).decode("ascii")
+        app = ServerApp.instance(
+            # Set the log level to debug for testing purposes
+            log_level='DEBUG',
+            port=http_port,
+            port_retries=0,
+            open_browser=False,
+            root_dir=str(root_dir),
+            base_url=base_url,
+            config=c,
+            allow_root=True,
+            token=token,
+            **kwargs
+        )
+
+        app.init_signal = lambda: None
+        app.log.propagate = True
+        app.log.handlers = []
+        # Initialize app without httpserver
+        app.initialize(argv=argv, new_httpserver=False)
+        app.log.propagate = True
+        app.log.handlers = []
+        # Start app without ioloop
+        app.start_app()
+        return app
+
+    return _configurable_serverapp
+
+
+@pytest.fixture
+def jp_ensure_app_fixture(request):
+    """Ensures that the 'app' fixture used by pytest-tornasync
+    is set to `jp_web_app`, the Tornado Web Application returned
+    by the ServerApp in Jupyter Server, provided by the jp_web_app
+    fixture in this module.
+
+    Note, this hardcodes the `app_fixture` option from
+    pytest-tornasync to `jp_web_app`. If this value is configured
+    to something other than the default, it will raise an exception.
+    """
+    app_option = request.config.getoption("app_fixture")
+    if app_option not in ["app", "jp_web_app"]:
+        raise Exception("jp_serverapp requires the `app-fixture` option "
+                        "to be set to 'jp_web_app`. Try rerunning the "
+                        "current tests with the option `--app-fixture "
+                        "jp_web_app`.")
+    elif app_option == "app":
+        # Manually set the app_fixture to `jp_web_app` if it's
+        # not set already.
+        request.config.option.app_fixture = "jp_web_app"
+
+
+@pytest.fixture(scope="function")
+def jp_serverapp(
+    jp_ensure_app_fixture,
+    jp_server_config,
+    jp_argv,
+    jp_configurable_serverapp
+):
+    """Starts a Jupyter Server instance based on the established configuration values."""
+    app = jp_configurable_serverapp(config=jp_server_config, argv=jp_argv)
+    yield app
+    app.remove_server_info_file()
+    app.remove_browser_open_file()
+    app.cleanup_kernels()
+
+
+@pytest.fixture
+def jp_web_app(jp_serverapp):
+    """app fixture is needed by pytest_tornasync plugin"""
+    return jp_serverapp.web_app
+
+
+@pytest.fixture
+def jp_auth_header(jp_serverapp):
+    """Configures an authorization header using the token from the serverapp fixture."""
+    return {"Authorization": "token {token}".format(token=jp_serverapp.token)}
+
+
+@pytest.fixture
+def jp_base_url():
+    """Returns the base url to use for the test."""
+    return "/a%40b/"
+
+
+@pytest.fixture
+def jp_fetch(jp_serverapp, http_server_client, jp_auth_header, jp_base_url):
+    """Sends an (asynchronous) HTTP request to a test server.
+
+    The fixture is a factory; it can be called like
+    a function inside a unit test. Here's a basic
+    example of how use this fixture:
+
+    .. code-block:: python
+
+        async def my_test(jp_fetch):
+
+            response = await jp_fetch("api", "spec.yaml")
+            ...
+    """
+    def client_fetch(*parts, headers={}, params={}, **kwargs):
+        # Handle URL strings
+        path_url = url_escape(url_path_join(*parts), plus=False)
+        base_path_url = url_path_join(jp_base_url, path_url)
+        params_url = urllib.parse.urlencode(params)
+        url = base_path_url + "?" + params_url
+        # Add auth keys to header
+        headers.update(jp_auth_header)
+        # Make request.
+        return http_server_client.fetch(
+            url, headers=headers, request_timeout=20, **kwargs
+        )
+    return client_fetch
+
+
+@pytest.fixture
+def jp_ws_fetch(jp_serverapp, jp_auth_header, jp_http_port, jp_base_url):
+    """Sends a websocket request to a test server.
+
+    The fixture is a factory; it can be called like
+    a function inside a unit test. Here's a basic
+    example of how use this fixture:
+
+    .. code-block:: python
+
+        async def my_test(jp_fetch, jp_ws_fetch):
+            # Start a kernel
+            r = await jp_fetch(
+                'api', 'kernels',
+                method='POST',
+                body=json.dumps({
+                    'name': "python3"
+                })
+            )
+            kid = json.loads(r.body.decode())['id']
+
+            # Open a websocket connection.
+            ws = await jp_ws_fetch(
+                'api', 'kernels', kid, 'channels'
+            )
+            ...
+    """
+    def client_fetch(*parts, headers={}, params={}, **kwargs):
+        # Handle URL strings
+        path_url = url_escape(url_path_join(*parts), plus=False)
+        base_path_url = url_path_join(jp_base_url, path_url)
+        urlparts = urllib.parse.urlparse('ws://localhost:{}'.format(jp_http_port))
+        urlparts = urlparts._replace(
+            path=base_path_url,
+            query=urllib.parse.urlencode(params)
+        )
+        url = urlparts.geturl()
+        # Add auth keys to header
+        headers.update(jp_auth_header)
+        # Make request.
+        req = tornado.httpclient.HTTPRequest(
+            url,
+            headers=jp_auth_header,
+            connect_timeout=120
+        )
+        return tornado.websocket.websocket_connect(req)
+    return client_fetch
+
+
+some_resource = u"The very model of a modern major general"
+sample_kernel_json = {
+    'argv':['cat', '{connection_file}'],
+    'display_name': 'Test kernel',
+}
+@pytest.fixture
+def jp_kernelspecs(jp_data_dir):
+    """Configures some sample kernelspecs in the Jupyter data directory."""
+    spec_names = ['sample', 'sample 2']
+    for name in spec_names:
+        sample_kernel_dir = jp_data_dir.joinpath('kernels', name)
+        sample_kernel_dir.mkdir(parents=True)
+        # Create kernel json file
+        sample_kernel_file = sample_kernel_dir.joinpath('kernel.json')
+        sample_kernel_file.write_text(json.dumps(sample_kernel_json))
+        # Create resources text
+        sample_kernel_resources = sample_kernel_dir.joinpath('resource.txt')
+        sample_kernel_resources.write_text(some_resource)
+
+
+@pytest.fixture(params=[True, False])
+def jp_contents_manager(request, tmp_path):
+    """Returns a FileContentsManager instance based on the use_atomic_writing parameter value."""
+    return FileContentsManager(root_dir=str(tmp_path), use_atomic_writing=request.param)
+
+
+@pytest.fixture
+def jp_large_contents_manager(tmp_path):
+    """Returns a LargeFileManager instance."""
+    return LargeFileManager(root_dir=str(tmp_path))
+
+
+@pytest.fixture
+def jp_create_notebook(jp_root_dir):
+    """Creates a notebook in the test's home directory."""
+    def inner(nbpath):
+        nbpath = jp_root_dir.joinpath(nbpath)
+        # Check that the notebook has the correct file extension.
+        if nbpath.suffix != '.ipynb':
+            raise Exception("File extension for notebook must be .ipynb")
+        # If the notebook path has a parent directory, make sure it's created.
+        parent = nbpath.parent
+        parent.mkdir(parents=True, exist_ok=True)
+        # Create a notebook string and write to file.
+        nb = nbformat.v4.new_notebook()
+        nbtext = nbformat.writes(nb, version=4)
+        nbpath.write_text(nbtext)
+    return inner
diff --git a/setup.py b/setup.py
index c79672055..063764d2a 100644
--- a/setup.py
+++ b/setup.py
@@ -52,7 +52,8 @@
     ],
     extras_require = {
         'test': ['coverage', 'requests',
-                 'pytest', 'pytest-cov', 'pytest-jupyter',
+                 'pytest', 'pytest-cov',
+                 'pytest-tornasync',
                  'pytest-console-scripts', 'ipykernel'],
     },
     python_requires = '>=3.6',
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 000000000..bdac3802b
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,3 @@
+pytest_plugins = [
+    "jupyter_server.pytest_plugin"
+]
diff --git a/tests/extension/test_handler.py b/tests/extension/test_handler.py
index 1f5b52e64..1e4a47c78 100644
--- a/tests/extension/test_handler.py
+++ b/tests/extension/test_handler.py
@@ -51,7 +51,7 @@ async def test_handler_template(jp_fetch, mock_template):
         }
     ]
 )
-async def test_handler_setting(jp_fetch):
+async def test_handler_setting(jp_fetch, jp_server_config):
     # Test that the extension trait was picked up by the webapp.
     r = await jp_fetch(
         'mock',
@@ -64,7 +64,7 @@ async def test_handler_setting(jp_fetch):
 @pytest.mark.parametrize(
     'jp_argv', (['--MockExtensionApp.mock_trait=test mock trait'],)
 )
-async def test_handler_argv(jp_fetch):
+async def test_handler_argv(jp_fetch, jp_argv):
     # Test that the extension trait was picked up by the webapp.
     r = await jp_fetch(
         'mock',
@@ -75,28 +75,31 @@ async def test_handler_argv(jp_fetch):
 
 
 @pytest.mark.parametrize(
-    'jp_server_config',
+    'jp_server_config,jp_base_url',
     [
-        {
-            "ServerApp": {
-                "jpserver_extensions": {
-                    "tests.extension.mockextensions": True
+        (
+            {
+                "ServerApp": {
+                    "jpserver_extensions": {
+                        "tests.extension.mockextensions": True
+                    },
+                    # Move extension handlers behind a url prefix
+                    "base_url": "test_prefix"
                 },
-                # Move extension handlers behind a url prefix
-                "base_url": "test_prefix"
+                "MockExtensionApp": {
+                    # Change a trait in the MockExtensionApp using
+                    # the following config value.
+                    "mock_trait": "test mock trait"
+                }
             },
-            "MockExtensionApp": {
-                # Change a trait in the MockExtensionApp using
-                # the following config value.
-                "mock_trait": "test mock trait"
-            }
-        }
+            '/test_prefix/'
+        )
     ]
 )
-async def test_base_url(jp_fetch):
+async def test_base_url(jp_fetch, jp_server_config, jp_base_url):
     # Test that the extension's handlers were properly prefixed
     r = await jp_fetch(
-        'test_prefix', 'mock',
+        'mock',
         method='GET'
     )
     assert r.code == 200
@@ -104,7 +107,6 @@ async def test_base_url(jp_fetch):
 
     # Test that the static namespace was prefixed by base_url
     r = await jp_fetch(
-        'test_prefix',
         'static', 'mockextension', 'mock.txt',
         method='GET'
     )
diff --git a/tests/extension/test_serverextension.py b/tests/extension/test_serverextension.py
index cc2fb80dd..2034d3279 100644
--- a/tests/extension/test_serverextension.py
+++ b/tests/extension/test_serverextension.py
@@ -106,7 +106,7 @@ def test_merge_config(
         }
     ]
 )
-def test_load_ordered(jp_serverapp):
+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"
diff --git a/tests/services/contents/test_api.py b/tests/services/contents/test_api.py
index ee8b57fb7..fea04db7b 100644
--- a/tests/services/contents/test_api.py
+++ b/tests/services/contents/test_api.py
@@ -264,24 +264,25 @@ async def test_get_bad_type(jp_fetch, contents):
         )
     assert expected_http_error(e, 400, '%s is not a directory' % path)
 
-
-def _check_created(r, contents_dir, path, name, type='notebook'):
-    fpath = path+'/'+name
-    assert r.code == 201
-    location = '/api/contents/' + tornado.escape.url_escape(fpath, plus=False)
-    assert r.headers['Location'] == location
-    model = json.loads(r.body.decode())
-    assert model['name'] == name
-    assert model['path'] == fpath
-    assert model['type'] == type
-    path = contents_dir + '/' + fpath
-    if type == 'directory':
-        assert pathlib.Path(path).is_dir()
-    else:
-        assert pathlib.Path(path).is_file()
-
-
-async def test_create_untitled(jp_fetch, contents, contents_dir):
+@pytest.fixture
+def _check_created(jp_base_url):
+    def _inner(r, contents_dir, path, name, type='notebook'):
+        fpath = path+'/'+name
+        assert r.code == 201
+        location = jp_base_url + 'api/contents/' + tornado.escape.url_escape(fpath, plus=False)
+        assert r.headers['Location'] == location
+        model = json.loads(r.body.decode())
+        assert model['name'] == name
+        assert model['path'] == fpath
+        assert model['type'] == type
+        path = contents_dir + '/' + fpath
+        if type == 'directory':
+            assert pathlib.Path(path).is_dir()
+        else:
+            assert pathlib.Path(path).is_file()
+    return _inner
+
+async def test_create_untitled(jp_fetch, contents, contents_dir, _check_created):
     path = 'å b'
     name = 'Untitled.ipynb'
     r = await jp_fetch(
@@ -309,7 +310,7 @@ async def test_create_untitled(jp_fetch, contents, contents_dir):
     _check_created(r, str(contents_dir), path, name, type='notebook')
 
 
-async def test_create_untitled_txt(jp_fetch, contents, contents_dir):
+async def test_create_untitled_txt(jp_fetch, contents, contents_dir, _check_created):
     name = 'untitled.txt'
     path = 'foo/bar'
     r = await jp_fetch(
@@ -329,7 +330,7 @@ async def test_create_untitled_txt(jp_fetch, contents, contents_dir):
     assert model['content'] == ''
 
 
-async def test_upload(jp_fetch, contents, contents_dir):
+async def test_upload(jp_fetch, contents, contents_dir, _check_created):
     nb = new_notebook()
     nbmodel = {'content': nb, 'type': 'notebook'}
     path = 'å b'
@@ -342,7 +343,7 @@ async def test_upload(jp_fetch, contents, contents_dir):
     _check_created(r, str(contents_dir), path, name)
 
 
-async def test_mkdir_untitled(jp_fetch, contents, contents_dir):
+async def test_mkdir_untitled(jp_fetch, contents, contents_dir, _check_created):
     name = 'Untitled Folder'
     path = 'å b'
     r = await jp_fetch(
@@ -370,7 +371,7 @@ async def test_mkdir_untitled(jp_fetch, contents, contents_dir):
     _check_created(r, str(contents_dir), path, name, type='directory')
 
 
-async def test_mkdir(jp_fetch, contents, contents_dir):
+async def test_mkdir(jp_fetch, contents, contents_dir, _check_created):
     name = 'New ∂ir'
     path = 'å b'
     r = await jp_fetch(
@@ -391,7 +392,7 @@ async def test_mkdir_hidden_400(jp_fetch):
     assert expected_http_error(e, 400)
 
 
-async def test_upload_txt(jp_fetch, contents, contents_dir):
+async def test_upload_txt(jp_fetch, contents, contents_dir, _check_created):
     body = 'ünicode téxt'
     model = {
         'content' : body,
@@ -418,7 +419,7 @@ async def test_upload_txt(jp_fetch, contents, contents_dir):
     assert model['content'] == body
 
 
-async def test_upload_b64(jp_fetch, contents, contents_dir):
+async def test_upload_b64(jp_fetch, contents, contents_dir, _check_created):
     body = b'\xFFblob'
     b64body = encodebytes(body).decode('ascii')
     model = {
@@ -446,7 +447,7 @@ async def test_upload_b64(jp_fetch, contents, contents_dir):
     assert decoded == body
 
 
-async def test_copy(jp_fetch, contents, contents_dir):
+async def test_copy(jp_fetch, contents, contents_dir, _check_created):
     path = 'å b'
     name = 'ç d.ipynb'
     copy = 'ç d-Copy1.ipynb'
@@ -476,7 +477,7 @@ async def test_copy(jp_fetch, contents, contents_dir):
     _check_created(r, str(contents_dir), path, copy3, type='notebook')
 
 
-async def test_copy_path(jp_fetch, contents, contents_dir):
+async def test_copy_path(jp_fetch, contents, contents_dir, _check_created):
     path1 = 'foo'
     path2 = 'å b'
     name = 'a.ipynb'
@@ -496,7 +497,7 @@ async def test_copy_path(jp_fetch, contents, contents_dir):
     _check_created(r, str(contents_dir), path2, copy, type='notebook')
 
 
-async def test_copy_put_400(jp_fetch, contents, contents_dir):
+async def test_copy_put_400(jp_fetch, contents, contents_dir, _check_created):
     with pytest.raises(tornado.httpclient.HTTPClientError) as e:
         await jp_fetch(
             'api', 'contents', 'å b/cøpy.ipynb',
@@ -506,7 +507,7 @@ async def test_copy_put_400(jp_fetch, contents, contents_dir):
     assert expected_http_error(e, 400)
 
 
-async def test_copy_dir_400(jp_fetch, contents, contents_dir):
+async def test_copy_dir_400(jp_fetch, contents, contents_dir, _check_created):
     with pytest.raises(tornado.httpclient.HTTPClientError) as e:
         await jp_fetch(
             'api', 'contents', 'foo',
@@ -517,7 +518,7 @@ async def test_copy_dir_400(jp_fetch, contents, contents_dir):
 
 
 @pytest.mark.parametrize('path,name', dirs)
-async def test_delete(jp_fetch, contents, contents_dir, path, name):
+async def test_delete(jp_fetch, contents, contents_dir, path, name, _check_created):
     nbname = name+'.ipynb'
     nbpath = (path + '/' + nbname).lstrip('/')
     r = await jp_fetch(
@@ -567,7 +568,7 @@ async def test_delete_non_empty_dir(jp_fetch, contents):
     assert expected_http_error(e, 404)
 
 
-async def test_rename(jp_fetch, contents, contents_dir):
+async def test_rename(jp_fetch, jp_base_url, contents, contents_dir):
     path = 'foo'
     name = 'a.ipynb'
     new_name = 'z.ipynb'
@@ -579,7 +580,7 @@ async def test_rename(jp_fetch, contents, contents_dir):
     )
     fpath = path+'/'+new_name
     assert r.code == 200
-    location = '/api/contents/' + fpath
+    location = url_path_join(jp_base_url, 'api/contents/', fpath)
     assert r.headers['Location'] == location
     model = json.loads(r.body.decode())
     assert model['name'] == new_name
diff --git a/tests/services/kernels/test_api.py b/tests/services/kernels/test_api.py
index 712ea8551..bc2ade403 100644
--- a/tests/services/kernels/test_api.py
+++ b/tests/services/kernels/test_api.py
@@ -31,18 +31,18 @@ async def test_no_kernels(jp_fetch):
     assert kernels == []
 
 
-async def test_default_kernels(jp_fetch):
+async def test_default_kernels(jp_fetch, jp_base_url):
     r = await jp_fetch(
         'api', 'kernels',
         method='POST',
         allow_nonstandard_methods=True
     )
     kernel = json.loads(r.body.decode())
-    assert r.headers['location'] == '/api/kernels/' + kernel['id']
+    assert r.headers['location'] == url_path_join(jp_base_url, '/api/kernels/', kernel['id'])
     assert r.code == 201
     assert isinstance(kernel, dict)
 
-    report_uri = '/api/security/csp-report'
+    report_uri = url_path_join(jp_base_url, '/api/security/csp-report')
     expected_csp = '; '.join([
         "frame-ancestors 'self'",
         'report-uri ' + report_uri,
@@ -51,7 +51,7 @@ async def test_default_kernels(jp_fetch):
     assert r.headers['Content-Security-Policy'] == expected_csp
 
 
-async def test_main_kernel_handler(jp_fetch):
+async def test_main_kernel_handler(jp_fetch, jp_base_url):
     # Start the first kernel
     r = await jp_fetch(
         'api', 'kernels',
@@ -61,11 +61,11 @@ async def test_main_kernel_handler(jp_fetch):
         })
     )
     kernel1 = json.loads(r.body.decode())
-    assert r.headers['location'] == '/api/kernels/' + kernel1['id']
+    assert r.headers['location'] == url_path_join(jp_base_url, '/api/kernels/', kernel1['id'])
     assert r.code == 201
     assert isinstance(kernel1, dict)
 
-    report_uri = '/api/security/csp-report'
+    report_uri = url_path_join(jp_base_url, '/api/security/csp-report')
     expected_csp = '; '.join([
         "frame-ancestors 'self'",
         'report-uri ' + report_uri,
diff --git a/tests/services/kernelspecs/test_api.py b/tests/services/kernelspecs/test_api.py
index e95e57f63..f5cc3a9a0 100644
--- a/tests/services/kernelspecs/test_api.py
+++ b/tests/services/kernelspecs/test_api.py
@@ -3,11 +3,8 @@
 
 import tornado
 
-from pytest_jupyter.jupyter_server import some_resource
-
 from jupyter_client.kernelspec import NATIVE_KERNEL_NAME
-
-from ...utils import expected_http_error
+from ...utils import expected_http_error, some_resource
 
 
 async def test_list_kernelspecs_bad(jp_fetch, jp_kernelspecs, jp_data_dir):
diff --git a/tests/services/sessions/test_api.py b/tests/services/sessions/test_api.py
index 6ffd01354..065e392a6 100644
--- a/tests/services/sessions/test_api.py
+++ b/tests/services/sessions/test_api.py
@@ -10,6 +10,8 @@
 from nbformat import writes
 
 from ...utils import expected_http_error
+from jupyter_server.utils import url_path_join
+
 
 j = lambda r: json.loads(r.body.decode())
 
@@ -148,7 +150,7 @@ def assert_session_equality(actual, expected):
     assert_kernel_equality(actual['kernel'], expected['kernel'])
 
 
-async def test_create(session_client):
+async def test_create(session_client, jp_base_url):
     # Make sure no sessions exist.
     resp = await session_client.list()
     sessions = j(resp)
@@ -161,7 +163,7 @@ async def test_create(session_client):
     assert 'id' in new_session
     assert new_session['path'] == 'foo/nb1.ipynb'
     assert new_session['type'] == 'notebook'
-    assert resp.headers['Location'] == '/api/sessions/' + new_session['id']
+    assert resp.headers['Location'] == url_path_join(jp_base_url, '/api/sessions/', new_session['id'])
 
     # Check that the new session appears in list.
     resp = await session_client.list()
@@ -209,7 +211,7 @@ async def test_create_deprecated(session_client):
     await session_client.cleanup()
 
 
-async def test_create_with_kernel_id(session_client, jp_fetch):
+async def test_create_with_kernel_id(session_client, jp_fetch, jp_base_url):
     # create a new kernel
     resp = await jp_fetch('api/kernels', method='POST', allow_nonstandard_methods=True)
     kernel = j(resp)
@@ -220,7 +222,7 @@ async def test_create_with_kernel_id(session_client, jp_fetch):
     assert 'id' in new_session
     assert new_session['path'] == 'foo/nb1.ipynb'
     assert new_session['kernel']['id'] == kernel['id']
-    assert resp.headers['Location'] == '/api/sessions/{0}'.format(new_session['id'])
+    assert resp.headers['Location'] == url_path_join(jp_base_url, '/api/sessions/{0}'.format(new_session['id']))
 
     resp = await session_client.list()
     sessions = j(resp)
diff --git a/tests/test_paths.py b/tests/test_paths.py
index 155426d06..60c2951a1 100644
--- a/tests/test_paths.py
+++ b/tests/test_paths.py
@@ -2,7 +2,7 @@
 import pytest
 import tornado
 from jupyter_server.base.handlers import path_regex
-
+from jupyter_server.utils import url_path_join
 
 # build regexps that tornado uses:
 path_pat = re.compile('^' + '/x%s' % path_regex + '$')
@@ -45,7 +45,7 @@ async def test_trailing_slash(jp_ensure_app_fixture, uri, expected, http_server_
     # http_server_client raises an exception when follow_redirects=False
     with pytest.raises(tornado.httpclient.HTTPClientError) as err:
         await http_server_client.fetch(
-            uri,
+            url_path_join(jp_base_url, uri),
             headers=jp_auth_header,
             request_timeout=20,
             follow_redirects=False
@@ -54,4 +54,4 @@ async def test_trailing_slash(jp_ensure_app_fixture, uri, expected, http_server_
     response = err.value.response
     assert response.code == 302
     assert "Location" in response.headers
-    assert response.headers["Location"] == expected
+    assert response.headers["Location"] == url_path_join(jp_base_url, expected)
diff --git a/tests/utils.py b/tests/utils.py
index 819d62aa5..8e7376897 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -1,6 +1,13 @@
 import json
 import tornado
 
+some_resource = u"The very model of a modern major general"
+
+sample_kernel_json = {
+    'argv':['cat', '{connection_file}'],
+    'display_name': 'Test kernel',
+}
+
 
 def mkdir(tmp_path, *parts):
     path = tmp_path.joinpath(*parts)