Revert "Disable unit test requiring isatty()"

This reverts commit 06b2b06.

test/test_config.c

@@ -185,6 +185,21 @@ static void flog_config_with_long_subsystem_option_and_no_subsystem_fails(void *
     assert_int_equal(error, FLOG_ERROR_OPTS);
 }
 
+static void
+flog_config_new_with_stdin_tty_and_no_message_args_fails(void **state) {
+    FlogError error = TEST_ERROR;
+    MOCK_ARGS(
+        TEST_PROGRAM_NAME,
+        TEST_OPTION_LEVEL_SHORT,
+        TEST_OPTION_LEVEL_VALUE_INFO
+    )
+
+    FlogConfig *config = flog_config_new(mock_argc, mock_argv, &error);
+
+    assert_null(config);
+    assert_int_equal(error, FLOG_ERROR_MSG);
+}
+
 static void
 flog_config_new_with_message_succeeds(void **state) {
     FlogError error = TEST_ERROR;
@@ -472,6 +487,7 @@ int main(void) {
         cmocka_unit_test(flog_config_new_with_long_category_opt_and_no_subsystem_opt_fails),
         cmocka_unit_test(flog_config_with_short_subsystem_option_and_no_subsystem_fails),
         cmocka_unit_test(flog_config_with_long_subsystem_option_and_no_subsystem_fails),
+        cmocka_unit_test(flog_config_new_with_stdin_tty_and_no_message_args_fails),
 
         // flog_config_new() success tests
         cmocka_unit_test(flog_config_new_with_message_succeeds),