+# AT_TEST($1: BISON-DIRECTIVES,
+# $2: MORE-BISON-DIRECTIVES,
+# $3: PARSER-ACTION,
+# $4: INPUT,
+# $5: SCANNER-ACTION,
+# $6: RESULT)
+# --------------------------------------
+# Check with and without %defines, to avoid regressions. It turns out
+# that in that case yacc.c calls the set-up of the %union twice,
+# because YYSTYPE is defined once in the header, and once in the
+# implementation file (eventually it'd be better to include the header
+# file, but that's another story). Unfortunately running these macros
+# a second time doubled the side-effects and resulted in a double
+# definition of the union members.
+m4_pushdef([AT_TEST],
+[_AT_TEST([$1], [$2], [$3], [$4], [$5], [$6])
+ _AT_TEST([$1 %defines], [$2], [$3], [$4], [$5], [$6])
+])
+