tests: Add lib/string-test test case

Show a basic example of how unit testing can be applied for the coreboot
project. Add a test harness for lib/string.c module.

TEST=Install cmocka via appropriate command:
sudo apt-get install -y libcmocka-dev
sudo emerge dev-util/cmocka
yum install libcmocka-devel
* Build and run unit tests via `make unit-tests`
* Check the output to see that tests passed.

Signed-off-by: Jan Dabros <jsd@semihalf.com>
Change-Id: Ibf5554d1e99a393721a66bdd35af0122c2e412c4
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40538
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Paul Fagerburg <pfagerburg@chromium.org>

tests/lib/Makefile.inc

@@ -0,0 +1,20 @@
+##
+## This file is part of the coreboot project.
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; version 2 of the License.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+
+# object filest should be under build/tests/ build/test/src/ build/test/run/
+# two examples - first should be simply string.c, second should use -wrap
+
+tests-y += string-test
+
+string-test-srcs += tests/lib/string-test.c
+string-test-srcs += src/lib/string.c

tests/lib/string-test.c

@@ -0,0 +1,53 @@
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <cmocka.h>
+
+#include <string.h>
+
+/*
+ * Important note: In every particular test, don't use any string-related
+ * functions other than function under test. We are linking against
+ * src/lib/string.c not the standard library. This is important for proper test
+ * isolation. One can use __builtin_xxx for many of the most simple str*()
+ * functions, when non-coreboot one is required.
+ */
+
+struct strings_t {
+	char *str;
+	size_t size;
+} strings[] = {
+	{"coreboot",	8},
+	{"is\0very",	2}, /* strlen should be 2 because of the embedded \0 */
+	{"nice\n",	5}
+};
+
+static void test_strlen_strings(void **state)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(strings); i++)
+		assert_int_equal(strings[i].size, strlen(strings[i].str));
+}
+
+static void test_strdup(void **state)
+{
+	char str[] = "Hello coreboot\n";
+	char *duplicate;
+
+	duplicate = strdup(str);
+
+	/* There is a more suitable Cmocka's function 'assert_string_equal()', but it
+	   is using strcmp() internally. */
+	assert_int_equal(0, memcmp(str, duplicate, __builtin_strlen(str)));
+}
+
+int main(void)
+{
+	const struct CMUnitTest tests[] = {
+		cmocka_unit_test(test_strlen_strings),
+		cmocka_unit_test(test_strdup),
+	};
+
+	return cmocka_run_group_tests(tests, NULL, NULL);
+}