Merge branch '2943-g-test-init-docs' into 'main'

gtestutils: Clarify docs about calling g_test_init() before anything

Closes #2943

See merge request GNOME/glib!3327

glib/gtestutils.c

@@ -89,11 +89,15 @@
  * The API is designed to handle creation and registration of test suites
  * and test cases implicitly. A simple call like
  * |[<!-- language="C" --> 
+ *   g_test_init (&argc, &argv, G_TEST_OPTION_ISOLATE_DIRS, NULL);
+ *
  *   g_test_add_func ("/misc/assertions", test_assertions);
  * ]|
  * creates a test suite called "misc" with a single test case named
  * "assertions", which consists of running the test_assertions function.
  *
+ * g_test_init() should be called before calling any other test functions.
+ *
  * In addition to the traditional g_assert_true(), the test framework provides
  * an extended set of assertions for comparisons: g_assert_cmpfloat(),
  * g_assert_cmpfloat_with_epsilon(), g_assert_cmpint(), g_assert_cmpuint(),
@@ -1684,6 +1688,8 @@ test_rm_isolate_dirs (void)
  * test random number generator, the name for g_get_prgname()
  * and parsing test related command line args.
  *
+ * This should be called before calling any other `g_test_*()` functions.
+ *
  * So far, the following arguments are understood:
  *
  * - `-l`: List test cases available in a test executable.