diff --git a/tests/mockserver.py b/tests/mockserver.py
index eb4f8334e..647b0682e 100644
--- a/tests/mockserver.py
+++ b/tests/mockserver.py
@@ -1,11 +1,13 @@
 import argparse
 import json
+import os
 import random
 import sys
 from pathlib import Path
 from shutil import rmtree
 from subprocess import PIPE, Popen
 from tempfile import mkdtemp
+from typing import Dict
 from urllib.parse import urlencode
 
 from OpenSSL import SSL
@@ -20,7 +22,6 @@ from twisted.web.static import File
 from twisted.web.util import redirectTo
 
 from scrapy.utils.python import to_bytes, to_unicode
-from scrapy.utils.test import get_testenv
 
 
 def getarg(request, name, default=None, type=None):
@@ -32,6 +33,16 @@ def getarg(request, name, default=None, type=None):
     return default
 
 
+def get_mockserver_env() -> Dict[str, str]:
+    """Return a OS environment dict suitable to run mockserver processes."""
+
+    tests_path = Path(__file__).parent.parent
+    pythonpath = str(tests_path) + os.pathsep + os.environ.get("PYTHONPATH", "")
+    env = os.environ.copy()
+    env["PYTHONPATH"] = pythonpath
+    return env
+
+
 # most of the following resources are copied from twisted.web.test.test_webclient
 class ForeverTakingResource(resource.Resource):
     """
@@ -264,7 +275,7 @@ class MockServer:
         self.proc = Popen(
             [sys.executable, "-u", "-m", "tests.mockserver", "-t", "http"],
             stdout=PIPE,
-            env=get_testenv(),
+            env=get_mockserver_env(),
         )
         http_address = self.proc.stdout.readline().strip().decode("ascii")
         https_address = self.proc.stdout.readline().strip().decode("ascii")
@@ -308,7 +319,7 @@ class MockDNSServer:
         self.proc = Popen(
             [sys.executable, "-u", "-m", "tests.mockserver", "-t", "dns"],
             stdout=PIPE,
-            env=get_testenv(),
+            env=get_mockserver_env(),
         )
         self.host = "127.0.0.1"
         self.port = int(
@@ -331,7 +342,7 @@ class MockFTPServer:
         self.proc = Popen(
             [sys.executable, "-u", "-m", "tests.ftpserver", "-d", str(self.path)],
             stderr=PIPE,
-            env=get_testenv(),
+            env=get_mockserver_env(),
         )
         for line in self.proc.stderr:
             if b"starting FTP server" in line:
diff --git a/tests/test_cmdline/__init__.py b/tests/test_cmdline/__init__.py
index 15833cd19..25ded143c 100644
--- a/tests/test_cmdline/__init__.py
+++ b/tests/test_cmdline/__init__.py
@@ -1,4 +1,5 @@
 import json
+import os
 import pstats
 import shutil
 import sys
@@ -14,6 +15,8 @@ from scrapy.utils.test import get_testenv
 class CmdlineTest(unittest.TestCase):
     def setUp(self):
         self.env = get_testenv()
+        tests_path = Path(__file__).parent.parent
+        self.env["PYTHONPATH"] += os.pathsep + str(tests_path.parent)
         self.env["SCRAPY_SETTINGS_MODULE"] = "tests.test_cmdline.settings"
 
     def _execute(self, *new_args, **kwargs):
diff --git a/tests/test_crawler.py b/tests/test_crawler.py
index 706bfbaa9..ecb9c9b62 100644
--- a/tests/test_crawler.py
+++ b/tests/test_crawler.py
@@ -1,4 +1,5 @@
 import logging
+import os
 import platform
 import subprocess
 import sys
@@ -23,8 +24,8 @@ from scrapy.spiderloader import SpiderLoader
 from scrapy.utils.log import configure_logging, get_scrapy_root_handler
 from scrapy.utils.misc import load_object
 from scrapy.utils.spider import DefaultSpider
-from scrapy.utils.test import get_crawler, get_testenv
-from tests.mockserver import MockServer
+from scrapy.utils.test import get_crawler
+from tests.mockserver import MockServer, get_mockserver_env
 
 
 class BaseCrawlerTest(unittest.TestCase):
@@ -289,12 +290,16 @@ class CrawlerRunnerHasSpider(unittest.TestCase):
 
 class ScriptRunnerMixin:
     script_dir: Path
+    cwd = os.getcwd()
 
     def run_script(self, script_name: str, *script_args):
         script_path = self.script_dir / script_name
         args = [sys.executable, str(script_path)] + list(script_args)
         p = subprocess.Popen(
-            args, env=get_testenv(), stdout=subprocess.PIPE, stderr=subprocess.PIPE
+            args,
+            env=get_mockserver_env(),
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
         )
         stdout, stderr = p.communicate()
         return stderr.decode("utf-8")
diff --git a/tests/test_proxy_connect.py b/tests/test_proxy_connect.py
index c05f4da91..dc0a82086 100644
--- a/tests/test_proxy_connect.py
+++ b/tests/test_proxy_connect.py
@@ -21,8 +21,6 @@ class MitmProxy:
     auth_pass = "scrapy"
 
     def start(self):
-        from scrapy.utils.test import get_testenv
-
         script = """
 import sys
 from mitmproxy.tools.main import mitmdump
@@ -46,7 +44,6 @@ sys.exit(mitmdump())
                 "--ssl-insecure",
             ],
             stdout=PIPE,
-            env=get_testenv(),
         )
         line = self.proc.stdout.readline().decode("utf-8")
         host_port = re.search(r"listening at http://([^:]+:\d+)", line).group(1)