Ensure that early = are not matched by the parser as invalid comparisons (GH-25375)

diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
index 78b11c9..0e6942f 100644
--- a/Lib/test/test_syntax.py
+++ b/Lib/test/test_syntax.py
@@ -863,6 +863,11 @@
    Traceback (most recent call last):
    SyntaxError: cannot assign to attribute here. Maybe you meant '==' instead of '='?
 
+Ensure that early = are not matched by the parser as invalid comparisons
+   >>> f(2, 4, x=34); {1,2 a}
+   Traceback (most recent call last):
+   SyntaxError: invalid syntax
+
 Make sure that the old "raise X, Y[, Z]" form is gone:
    >>> raise X, Y
    Traceback (most recent call last):