diff --git a/src/calibre/db/tests/main.py b/src/calibre/db/tests/main.py
index 85f358a383..e3afe467b1 100644
--- a/src/calibre/db/tests/main.py
+++ b/src/calibre/db/tests/main.py
@@ -6,13 +6,11 @@ __license__   = 'GPL v3'
 __copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
-import os
-from calibre.utils.run_tests import find_tests_in_dir, run_tests
+from calibre.utils.run_tests import find_tests_in_package, run_tests
 
 
 def find_tests():
-    base = os.path.dirname(os.path.abspath(__file__))
-    return find_tests_in_dir(base)
+    return find_tests_in_package('calibre.db.tests')
 
 
 if __name__ == '__main__':
diff --git a/src/calibre/ebooks/oeb/polish/tests/main.py b/src/calibre/ebooks/oeb/polish/tests/main.py
index 33aa02bc8d..f8a78fb2b8 100644
--- a/src/calibre/ebooks/oeb/polish/tests/main.py
+++ b/src/calibre/ebooks/oeb/polish/tests/main.py
@@ -5,13 +5,11 @@
 __license__ = 'GPL v3'
 __copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 
-import os
-from calibre.utils.run_tests import find_tests_in_dir, run_tests
+from calibre.utils.run_tests import find_tests_in_package, run_tests
 
 
 def find_tests():
-    base = os.path.dirname(os.path.abspath(__file__))
-    return find_tests_in_dir(base)
+    return find_tests_in_package('calibre.ebooks.oeb.polish.tests')
 
 
 if __name__ == '__main__':
diff --git a/src/calibre/srv/tests/main.py b/src/calibre/srv/tests/main.py
index 4da0b0a6e3..63d3b14e5f 100644
--- a/src/calibre/srv/tests/main.py
+++ b/src/calibre/srv/tests/main.py
@@ -5,13 +5,11 @@
 __license__ = 'GPL v3'
 __copyright__ = '2015, Kovid Goyal <kovid at kovidgoyal.net>'
 
-import os
-from calibre.utils.run_tests import find_tests_in_dir, run_tests
+from calibre.utils.run_tests import find_tests_in_package, run_tests
 
 
 def find_tests():
-    base = os.path.dirname(os.path.abspath(__file__))
-    return find_tests_in_dir(base)
+    return find_tests_in_package('calibre.srv.tests')
 
 
 if __name__ == '__main__':
diff --git a/src/calibre/utils/run_tests.py b/src/calibre/utils/run_tests.py
index 676667152e..c6c36c4253 100644
--- a/src/calibre/utils/run_tests.py
+++ b/src/calibre/utils/run_tests.py
@@ -3,7 +3,7 @@
 # License: GPLv3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
 
 
-import unittest, functools, os, importlib, zipfile
+import unittest, functools, importlib
 from calibre.utils.monotonic import monotonic
 
 
@@ -53,20 +53,9 @@ class TestResult(unittest.TextTestResult):
                 self.stream.writeln('\nSlowest tests: %s' % ' '.join(slowest))
 
 
-def find_tests_in_dir(path, excludes=('main.py',)):
-    if not os.path.exists(path) and '.zip' in path:
-        idx = path.rfind('.zip')
-        zf = path[:idx+4]
-        prefix = os.path.relpath(path, zf).replace(os.sep, '/')
-        package = prefix.replace('/', '.')
-        with zipfile.ZipFile(zf) as f:
-            namelist = f.namelist()
-        items = [i for i in namelist if i.startswith(prefix) and i.count('/') == prefix.count('/') + 1]
-    else:
-        d = os.path.dirname
-        base = d(d(d(os.path.abspath(__file__))))
-        package = os.path.relpath(path, base).replace(os.sep, '/').replace('/', '.')
-        items = os.listdir(path)
+def find_tests_in_package(package, excludes=('main.py',)):
+    loader = importlib.import_module(package).__spec__.loader
+    items = list(loader.contents())
     suits = []
     for x in items:
         if x.endswith('.py') and x not in excludes:
diff --git a/src/tinycss/tests/main.py b/src/tinycss/tests/main.py
index 3bef849f33..364172080b 100644
--- a/src/tinycss/tests/main.py
+++ b/src/tinycss/tests/main.py
@@ -5,12 +5,13 @@
 __license__ = 'GPL v3'
 __copyright__ = '2014, Kovid Goyal <kovid at kovidgoyal.net>'
 
-import unittest, os, argparse
+import unittest, argparse
+
 
 def find_tests():
-    from calibre.utils.run_tests import find_tests_in_dir
-    base = os.path.dirname(os.path.abspath(__file__))
-    return find_tests_in_dir(base)
+    from calibre.utils.run_tests import find_tests_in_package
+    return find_tests_in_package('tinycss.tests')
+
 
 def run_tests(find_tests=find_tests, for_build=False):
     if not for_build:
@@ -36,7 +37,7 @@ def run_tests(find_tests=find_tests, for_build=False):
         except StopIteration:
             pass
         if ans is None:
-            print ('No test named %s found' % args.name)
+            print('No test named %s found' % args.name)
             raise SystemExit(1)
         tests = ans
     else:
@@ -50,7 +51,6 @@ def run_tests(find_tests=find_tests, for_build=False):
     if for_build and result.errors or result.failures:
         raise SystemExit(1)
 
+
 if __name__ == '__main__':
     run_tests()
-
-