diff --git a/frontend_tests/run-casper b/frontend_tests/run-casper
index 7544eb3ece..8229e7b984 100755
--- a/frontend_tests/run-casper
+++ b/frontend_tests/run-casper
@@ -66,7 +66,7 @@ sys.path.insert(0, ZULIP_PATH)
 from tools.lib import sanity_check
 sanity_check.check_venv(__file__)
 
-from tools.lib.test_script import assert_provisioning_status_ok
+from tools.lib.test_script import assert_provisioning_status_ok, find_js_test_files
 from tools.lib.test_server import test_server_running
 
 from typing import Iterable, List
@@ -88,18 +88,7 @@ def reset_database() -> None:
 
 def run_tests(files: Iterable[str], external_host: str) -> None:
     test_dir = os.path.join(ZULIP_PATH, 'frontend_tests/casper_tests')
-    test_files = []
-    for file in files:
-        for file_name in os.listdir(test_dir):
-            if file_name.startswith(file):
-                file = file_name
-                break
-        if not os.path.exists(file):
-            file = os.path.join(test_dir, file)
-        test_files.append(os.path.abspath(file))
-
-    if not test_files:
-        test_files = sorted(glob.glob(os.path.join(test_dir, '*.js')))
+    test_files = find_js_test_files(test_dir, files)
 
     # 10-admin.js is too flaky!
     if options.skip_flaky:
diff --git a/tools/lib/test_script.py b/tools/lib/test_script.py
index 3f685a3674..62da587bc0 100644
--- a/tools/lib/test_script.py
+++ b/tools/lib/test_script.py
@@ -1,10 +1,11 @@
-from typing import Optional, Tuple
+from typing import Optional, Tuple, Iterable, List
 
 import os
 import sys
 from distutils.version import LooseVersion
 from version import PROVISION_VERSION
 from scripts.lib.zulip_tools import get_dev_uuid_var_path
+import glob
 
 def get_major_version(v: str) -> int:
     return int(v.split('.')[0])
@@ -77,3 +78,20 @@ def assert_provisioning_status_ok(force: bool) -> None:
             print(msg)
             print('If you really know what you are doing, use --force to run anyway.')
             sys.exit(1)
+
+
+def find_js_test_files(test_dir: str, files: Iterable[str]) -> List[str]:
+    test_files = []
+    for file in files:
+        for file_name in os.listdir(test_dir):
+            if file_name.startswith(file):
+                file = file_name
+                break
+        if not os.path.exists(file):
+            file = os.path.join(test_dir, file)
+        test_files.append(os.path.abspath(file))
+
+    if not test_files:
+        test_files = sorted(glob.glob(os.path.join(test_dir, '*.js')))
+
+    return test_files
diff --git a/tools/test-js-with-puppeteer b/tools/test-js-with-puppeteer
index 38c13c5290..3c61856dac 100755
--- a/tools/test-js-with-puppeteer
+++ b/tools/test-js-with-puppeteer
@@ -38,7 +38,7 @@ sys.path.insert(0, ZULIP_PATH)
 from tools.lib import sanity_check
 sanity_check.check_venv(__file__)
 
-from tools.lib.test_script import assert_provisioning_status_ok
+from tools.lib.test_script import assert_provisioning_status_ok, find_js_test_files
 from tools.lib.test_server import test_server_running
 
 from typing import Iterable
@@ -56,18 +56,7 @@ for f in glob.glob('var/puppeteer/puppeteer-failure*.png'):
 
 def run_tests(files: Iterable[str], external_host: str) -> None:
     test_dir = os.path.join(ZULIP_PATH, 'frontend_tests/puppeteer_tests')
-    test_files = []
-    for file in files:
-        for file_name in os.listdir(test_dir):
-            if file_name.startswith(file):
-                file = file_name
-                break
-        if not os.path.exists(file):
-            file = os.path.join(test_dir, file)
-        test_files.append(os.path.abspath(file))
-
-    if not test_files:
-        test_files = sorted(glob.glob(os.path.join(test_dir, '*.js')))
+    test_files = find_js_test_files(test_dir, files)
 
     def run_tests() -> int:
         ret = 1