Test for special syntax error for elif following else

Author: swfarnsworth

Lib/test/test_syntax.py

@@ -918,6 +918,18 @@
      ...
    SyntaxError: 'break' outside loop
 
+elif can't come after an else.
+
+    >>> if a % 2 == 0:
+    ...     pass
+    ... else:
+    ...     pass
+    ... elif a % 2 == 1:
+    ...     pass
+    Traceback (most recent call last):
+      ...
+    SyntaxError: 'elif' block follows an 'else' block
+
 Misuse of the nonlocal and global statement can lead to a few unique syntax errors.
 
    >>> def f():