syntax/parse: add test for non-tilde pattern expander

pkgs/racket-test/tests/stxparse/test.rkt

@@ -591,6 +591,33 @@
                                      (+ x y z))))
                   (syntax->datum #'(let ([x 1] [y 2] [z 3])
                                      (+ x y z))))
+
+    (define-syntax sep-comma ; test pattern expanders that don't begin with tilde
+      (pattern-expander
+       (lambda (stx)
+         (syntax-case stx ()
+           [(sep-comma pat)
+            (with-syntax ([ooo '...])
+              #'((~seq (~or (~and pat (~not ((~datum unquote) _))) ((~datum unquote) pat))
+                       (~or (~peek-not _) (~peek ((~datum unquote) _))))
+                 ooo))]))))
+
+    (define-splicing-syntax-class bindings2
+      [pattern (sep-comma [b:binding])
+               #:with (name ...) #'(b.name ...)
+               #:with (expr ...) #'(b.expr ...)])
+
+    (define (parse-my-let2 stx)
+      (syntax-parse stx
+        [(_ bs:bindings2 body)
+         #'(let ([bs.name bs.expr] ...)
+             body)]))
+
+    (check-equal? (syntax->datum
+                   (parse-my-let2 #'(my-let ([x = 1], [y = 2], [z = 3])
+                                      (+ x y z))))
+                  (syntax->datum #'(let ([x 1] [y 2] [z 3])
+                                     (+ x y z))))
     ))
 
 (test-case "this-syntax"