Exclude code-style test automatically if pycodestyle is not installed.

runtests.py

@@ -2446,6 +2446,12 @@ def runtests(options, cmd_args, coverage=None):
             test_suite.addTest(filetests.handle_directory(sys_pyregr_dir, 'pyregr'))
 
     if options.code_style and options.shard_num <= 0:
+        try:
+            import pycodestyle
+        except ImportError:
+            # Hack to make the exclusion visible.
+            missing_dep_excluder.tests_missing_deps.append('TestCodeFormat')
+        else:
             test_suite.addTest(TestCodeFormat(options.cython_dir))
 
     if xml_output_dir: