handle explicit line joining

pycodestyle.py

@@ -892,6 +892,9 @@ def missing_whitespace(logical_line, tokens):
                 # tuple (and list for some reason?)
                 elif text == ',' and next_char in ')]':
                     pass
+                # explicit line joining
+                elif text == ',' and next_char in '\\':
+                    pass
                 else:
                     yield start, f'E231 missing whitespace after {text!r}'
 

tests/test_E231.py

@@ -0,0 +1,14 @@
+import unittest
+
+from testing.support import errors_from_src
+
+
+class E231Test(unittest.TestCase):
+    def test_E231(self):
+        result = errors_from_src("""\
+with test(),\\
+        test(),     \\
+        test():
+    pass
+""")
+        self.assertEqual(result, [])