scripts: tests: Blackbox test expansion - testlist

Adds tests related to the flags creating testlists:
* -E, --save-tests
* -F, --load-tests

Signed-off-by: Lukasz Mrugala <lukaszx.mrugala@intel.com>

scripts/tests/twister_blackbox/test_testlist.py

diff --git a/scripts/tests/twister_blackbox/test_testlist.py b/scripts/tests/twister_blackbox/test_testlist.py
new file mode 100644
index 0000000..abbf101
--- /dev/null
+++ b/scripts/tests/twister_blackbox/test_testlist.py
@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+# Copyright (c) 2024 Intel Corporation
+#
+# SPDX-License-Identifier: Apache-2.0
+"""
+Blackbox tests for twister's command line functions related to saving and loading a testlist.
+"""
+
+import importlib
+import mock
+import os
+import pytest
+import sys
+import json
+
+from conftest import ZEPHYR_BASE, TEST_DATA, testsuite_filename_mock, clear_log_in_test
+from twisterlib.testplan import TestPlan
+
+
+class TestTestlist:
+    @classmethod
+    def setup_class(cls):
+        apath = os.path.join(ZEPHYR_BASE, 'scripts', 'twister')
+        cls.loader = importlib.machinery.SourceFileLoader('__main__', apath)
+        cls.spec = importlib.util.spec_from_loader(cls.loader.name, cls.loader)
+        cls.twister_module = importlib.util.module_from_spec(cls.spec)
+
+    @classmethod
+    def teardown_class(cls):
+        pass
+
+    @mock.patch.object(TestPlan, 'TESTSUITE_FILENAME', testsuite_filename_mock)
+    def test_save_tests(self, out_path):
+        test_platforms = ['qemu_x86', 'frdm_k64f']
+        path = os.path.join(TEST_DATA, 'tests', 'dummy', 'agnostic')
+        saved_tests_file_path = os.path.realpath(os.path.join(out_path, '..', 'saved-tests.json'))
+        args = ['-i', '--outdir', out_path, '-T', path, '-y'] + \
+               ['--save-tests', saved_tests_file_path] + \
+               [val for pair in zip(
+                   ['-p'] * len(test_platforms), test_platforms
+               ) for val in pair]
+
+        # Save agnostics tests
+        with mock.patch.object(sys, 'argv', [sys.argv[0]] + args), \
+                pytest.raises(SystemExit) as sys_exit:
+            self.loader.exec_module(self.twister_module)
+
+        assert str(sys_exit.value) == '0'
+
+        clear_log_in_test()
+
+        # Load all
+        path = os.path.join(TEST_DATA, 'tests', 'dummy')
+        args = ['-i', '--outdir', out_path, '-T', path, '-y'] + \
+               ['--load-tests', saved_tests_file_path] + \
+               [val for pair in zip(
+                   ['-p'] * len(test_platforms), test_platforms
+               ) for val in pair]
+
+        with mock.patch.object(sys, 'argv', [sys.argv[0]] + args), \
+                pytest.raises(SystemExit) as sys_exit:
+            self.loader.exec_module(self.twister_module)
+
+        assert str(sys_exit.value) == '0'
+
+        with open(os.path.join(out_path, 'testplan.json')) as f:
+            j = json.load(f)
+        filtered_j = [
+           (ts['platform'], ts['name'], tc['identifier']) \
+               for ts in j['testsuites'] \
+               for tc in ts['testcases'] if 'reason' not in tc
+        ]
+
+        assert len(filtered_j) == 5