Use parameterized to enable parallelisation of slow tests

We can't use pytest's parameterisation here as this test is a
unittest-style test, to which pytest does not support applying
parameterisation. Instead we can use the separate parameterized
package which offers parameterisation on plain unittest tests,
including when run under pytest.

Happily this also plays nicely with pytest-xdist. As the resulting
test functions are actually separate functions on the class, xdist
is able to then spread the work between workers.

setup.cfg

@@ -48,6 +48,7 @@ test =
     astroid >=2, <4; python_version >= "3"
     pytest
     pytest-xdist
+    parameterized
 
 [options.package_data]
 asttokens = py.typed

tests/test_mark_tokens.py

@@ -5,13 +5,12 @@
 import inspect
 import io
 import os
+from parameterized import parameterized
 import re
 import sys
 import textwrap
 import token
-from typing import List
 import unittest
-from time import time
 
 import astroid
 import six
@@ -630,7 +629,15 @@ def test_complex_slice_and_parens(self):
     self.create_mark_checker(source)
 
   if six.PY3:
-    def test_sys_modules(self):
+    def _parameterize_sys_modules():
+      modules = list(sys.modules.keys())
+      if not os.environ.get('ASTTOKENS_SLOW_TESTS'):
+        modules = modules[:20]
+
+      return parameterized.expand([(x,) for x in modules])
+
+    @_parameterize_sys_modules()
+    def test_sys_modules(self, module_name):
       """
       Verify all nodes on source files obtained from sys.modules.
       This can take a long time as there are many modules,
@@ -639,51 +646,42 @@ def test_sys_modules(self):
       """
       from .test_astroid import AstroidTreeException
 
-      modules = list(sys.modules.values())
-      if not os.environ.get('ASTTOKENS_SLOW_TESTS'):
-        modules = modules[:20]
+      module = sys.modules[module_name]
+
+      try:
+        filename = inspect.getsourcefile(module)
+      except Exception:  # some modules raise weird errors
+        self.skipTest("Failed to get source file")
+
+      if not filename:
+        self.skipTest("No source file for module")
+
+      filename = os.path.abspath(filename)
+      print(filename)
+      try:
+        with io.open(filename) as f:
+          source = f.read()
+      except OSError:
+        self.skipTest("Error reading source file")
+
+      if self.is_astroid_test and (
+          # Astroid fails with a syntax error if a type comment is on its own line
+          re.search(r'^\s*# type: ', source, re.MULTILINE)
+      ):
+        self.skipTest("Skipping potential Astroid syntax error")
+
+      try:
+        self.create_mark_checker(source)
+      except AstroidTreeException:
+        # Astroid sometimes fails with errors like:
+        #     AttributeError: 'TreeRebuilder' object has no attribute 'visit_typealias'
+        # See https://github.com/gristlabs/asttokens/actions/runs/6015907789/job/16318767911?pr=110
+        # Should be fixed in the next astroid release:
+        #     https://github.com/pylint-dev/pylint/issues/8782#issuecomment-1669967220
+        # Note that this exception is raised before asttokens is even involved,
+        # it's purely an astroid bug that we can safely ignore.
+        self.skipTest("Skipping Astroid error")
 
-      start = time()
-      for module in modules:
-        # Don't let this test (which runs twice) take longer than 13 minutes
-        # to avoid the travis build time limit of 30 minutes
-        if time() - start > 13 * 60:
-          break
-
-        try:
-          filename = inspect.getsourcefile(module)
-        except Exception:  # some modules raise weird errors
-          continue
-
-        if not filename:
-          continue
-
-        filename = os.path.abspath(filename)
-        print(filename)
-        try:
-          with io.open(filename) as f:
-            source = f.read()
-        except OSError:
-          continue
-
-        if self.is_astroid_test and (
-            # Astroid fails with a syntax error if a type comment is on its own line
-            re.search(r'^\s*# type: ', source, re.MULTILINE)
-        ):
-          print('Skipping', filename)
-          continue
-
-        try:
-          self.create_mark_checker(source)
-        except AstroidTreeException:
-          # Astroid sometimes fails with errors like:
-          #     AttributeError: 'TreeRebuilder' object has no attribute 'visit_typealias'
-          # See https://github.com/gristlabs/asttokens/actions/runs/6015907789/job/16318767911?pr=110
-          # Should be fixed in the next astroid release:
-          #     https://github.com/pylint-dev/pylint/issues/8782#issuecomment-1669967220
-          # Note that this exception is raised before asttokens is even involved,
-          # it's purely an astroid bug that we can safely ignore.
-          continue
 
   if six.PY3:
     def test_dict_merge(self):