Skip a sysconfig test if _ctypes is not available.

Also migrates test_sysconfig to unittest discovery.

Lib/test/test_sysconfig.py

@@ -5,7 +5,7 @@ import subprocess
 import shutil
 from copy import copy
 
-from test.support import (run_unittest, TESTFN, unlink, check_warnings,
+from test.support import (import_module, TESTFN, unlink, check_warnings,
                           captured_stdout, skip_unless_symlink, change_cwd)
 
 import sysconfig
@@ -387,7 +387,8 @@ class TestSysConfig(unittest.TestCase):
 
     @unittest.skipUnless(sys.platform == 'linux', 'Linux-specific test')
     def test_triplet_in_ext_suffix(self):
-        import ctypes, platform, re
+        ctypes = import_module('ctypes')
+        import platform, re
         machine = platform.machine()
         suffix = sysconfig.get_config_var('EXT_SUFFIX')
         if re.match('(aarch64|arm|mips|ppc|powerpc|s390|sparc)', machine):
@@ -435,8 +436,5 @@ class MakefileTests(unittest.TestCase):
         })
 
 
-def test_main():
-    run_unittest(TestSysConfig, MakefileTests)
-
 if __name__ == "__main__":
-    test_main()
+    unittest.main()