Make default double serializer ignore userdata again

The user might want to use the userdata for something different, so the
serializer should ignore it by default.

Explicitly setting the serializer to json_object_double_to_json_string will
still make it interpret the userdata as a format string.

tests/Makefile.am

@@ -11,6 +11,7 @@ TESTS+= testReplaceExisting.test
 TESTS+= test_parse_int64.test
 TESTS+= test_null.test
 TESTS+= test_cast.test
+TESTS+= test_double_serializer.test
 TESTS+= test_parse.test
 TESTS+= test_locale.test
 TESTS+= test_charcase.test
@@ -22,7 +23,7 @@ check_PROGRAMS=
 check_PROGRAMS += $(TESTS:.test=)
 
 # Note: handled by test1.test
-check_PROGRAMS += test1Formatted 
+check_PROGRAMS += test1Formatted
 test1Formatted_SOURCES = test1.c parse_flags.c
 test1Formatted_CPPFLAGS = -DTEST_FORMATTED
 

tests/test_double_serializer.c

@@ -0,0 +1,31 @@
+/*
+* Tests if the format string for double serialization is handled correctly
+*/
+
+#include <stdio.h>
+#include "config.h"
+
+#include "json_object.h"
+#include "json_object_private.h"
+
+int main()
+{
+	struct json_object *obj = json_object_new_double(0.5);
+
+	printf("Test default serializer:\n");
+	printf("obj.to_string(standard)=%s\n", json_object_to_json_string(obj));
+
+	printf("Test default serializer with custom userdata:\n");
+	obj->_userdata = "test";
+	printf("obj.to_string(userdata)=%s\n", json_object_to_json_string(obj));
+
+	printf("Test explicit serializer with custom userdata:\n");
+	json_object_set_serializer(obj, json_object_double_to_json_string, "test", NULL);
+	printf("obj.to_string(custom)=%s\n", json_object_to_json_string(obj));
+
+	printf("Test reset serializer:\n");
+	json_object_set_serializer(obj, NULL, NULL, NULL);
+	printf("obj.to_string(reset)=%s\n", json_object_to_json_string(obj));
+
+	json_object_put(obj);
+}

tests/test_double_serializer.expected

@@ -0,0 +1,8 @@
+Test default serializer:
+obj.to_string(standard)=0.5
+Test default serializer with custom userdata:
+obj.to_string(userdata)=0.5
+Test explicit serializer with custom userdata:
+obj.to_string(custom)=test
+Test reset serializer:
+obj.to_string(reset)=0.5

tests/test_double_serializer.test

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+# Common definitions
+if test -z "$srcdir"; then
+    srcdir="${0%/*}"
+    test "$srcdir" = "$0" && srcdir=.
+    test -z "$srcdir" && srcdir=.
+fi
+. "$srcdir/test-defs.sh"
+
+run_output_test test_double_serializer
+exit $?