tests: Clean up double comparisons to avoid compiler warning

To enable -Wformat-overflow=2, we need to clean up a couple of false
positives:

[2/5] Compiling C object tests/unit/test-qobject-output-visitor.p/test-qobject-output-visitor.c.o
../tests/unit/test-qobject-output-visitor.c: In function ‘test_visitor_out_list_struct’:
../tests/unit/test-qobject-output-visitor.c:577:28: error: ‘%.6f’ directive writing between 3 and 317 bytes into a region of size 32 [-Werror=format-overflow=]
  577 |         sprintf(expected, "%.6f", (double)i / 3);
      |                            ^~~~
../tests/unit/test-qobject-output-visitor.c:577:27: note: assuming directive output of 8 bytes
  577 |         sprintf(expected, "%.6f", (double)i / 3);
      |                           ^~~~~~
In file included from /usr/include/stdio.h:970,
                 from /home/me/q/var/qemu/include/qemu/osdep.h:114,
                 from ../tests/unit/test-qobject-output-visitor.c:13:
In function ‘sprintf’,
    inlined from ‘test_visitor_out_list_struct’ at ../tests/unit/test-qobject-output-visitor.c:577:9:
/usr/include/bits/stdio2.h:30:10: note: ‘__builtin___sprintf_chk’ output between 4 and 318 bytes into a destination of size 32
   30 |   return __builtin___sprintf_chk (__s, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   31 |                                   __glibc_objsize (__s), __fmt,
      |                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   32 |                                   __va_arg_pack ());
      |                                   ~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
FAILED: tests/unit/test-qobject-output-visitor.p/test-qobject-output-visitor.c.o

These buffers cannot actually overflow because the doubles are
between 0 and 31.0/3 inclusive.

However, formatting doubles just to compare them is silly.  Compare
them directly instead.  To avoid potential rounding trouble, change
the numbers tested to be representable exactly in double.

Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20260305-nvme-v4-3-b65b9de1839f@rsg.ci.i.u-tokyo.ac.jp>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

tests/unit/test-qobject-input-visitor.c

@@ -500,7 +500,7 @@ static void test_visitor_in_list_struct(TestInputVisitorData *data,
     g_string_append_printf(json, "'number': [");
     sep = "";
     for (i = 0; i < 32; i++) {
-        g_string_append_printf(json, "%s%f", sep, (double)i / 3);
+        g_string_append_printf(json, "%s%f", sep, (double)i / FLT_RADIX);
         sep = ", ";
     }
     g_string_append_printf(json, "], ");
@@ -583,11 +583,7 @@ static void test_visitor_in_list_struct(TestInputVisitorData *data,
 
     i = 0;
     for (num_list = arrs->number; num_list; num_list = num_list->next) {
-        char expected[32], actual[32];
-
-        sprintf(expected, "%.6f", (double)i / 3);
-        sprintf(actual, "%.6f", num_list->value);
-        g_assert_cmpstr(expected, ==, actual);
+        g_assert_cmpfloat(num_list->value, ==, (double)i / FLT_RADIX);
         i++;
     }
 

tests/unit/test-qobject-output-visitor.c

@@ -538,7 +538,7 @@ static void test_visitor_out_list_struct(TestOutputVisitorData *data,
     }
 
     for (i = 31; i >= 0; i--) {
-        QAPI_LIST_PREPEND(arrs->number, (double)i / 3);
+        QAPI_LIST_PREPEND(arrs->number, (double)i / FLT_RADIX);
     }
 
     for (i = 31; i >= 0; i--) {
@@ -571,12 +571,9 @@ static void test_visitor_out_list_struct(TestOutputVisitorData *data,
     i = 0;
     QLIST_FOREACH_ENTRY(qlist, e) {
         QNum *qvalue = qobject_to(QNum, qlist_entry_obj(e));
-        char expected[32], actual[32];
 
         g_assert(qvalue);
-        sprintf(expected, "%.6f", (double)i / 3);
-        sprintf(actual, "%.6f", qnum_get_double(qvalue));
-        g_assert_cmpstr(actual, ==, expected);
+        g_assert_cmpfloat(qnum_get_double(qvalue), ==, (double)i / FLT_RADIX);
         i++;
     }