tests: pytest: add an example for pytest

In this example, python test case get the running directory by handling
the "--cmdopt" option passed by pytest.

Signed-off-by: YouhuaX Zhu <youhuax.zhu@intel.com>

samples/subsys/testsuite/pytest/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.13.1)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(pytest_sample)
+
+target_sources(app PRIVATE src/main.c)

samples/subsys/testsuite/pytest/prj.conf

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+CONFIG_ZTEST=y
+CONFIG_IDLE_STACK_SIZE=4096

samples/subsys/testsuite/pytest/pytest/conftest.py

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+# Copyright (c) 2020 Intel Corporation.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+import pytest
+
+# add option "--comdopt" to pytest, or it will report "unknown option"
+# this option is passed from twister.
+def pytest_addoption(parser):
+    parser.addoption(
+        '--cmdopt'
+    )
+
+# define fixture to return value of option "--cmdopt", this fixture
+# will be requested by other fixture of tests.
+@pytest.fixture()
+def cmdopt(request):
+    return request.config.getoption('--cmdopt')

samples/subsys/testsuite/pytest/pytest/test_sample.py

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+# Copyright (c) 2020 Intel Corporation.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+import os
+import pytest
+
+# fixture cmdopt defined in conftest.py, it can be requested either in
+# tests or in other fixtures
+
+@pytest.fixture(autouse=True)
+def pytest_cmdopt_handle(cmdopt):
+    ''' An auto fixture, all tests automatically request this fixture.
+        Argument "cmdopt" is a fixture defined in conftest.py, it returns
+        the value of an option passed by twister, this fixture export
+        that value to environment.
+    '''
+    print("handle cmdopt:")
+    print(cmdopt)
+    data_path = cmdopt
+    os.environ['data_path'] = str(data_path)
+
+def test_case(cmdopt):
+    ''' Test cases make use of fixture cmdopt to get the value of "--cmdopt" option
+        passed by twister. Actually, fixture cmdopt returns a path of the directory
+        which holds the artifacts generated by ztest. The main work of test cases
+        in this file is to check those stuff in that directory.
+        This test case simply compare the return value of cmdopt with the
+        environment varialbe exported by fixture pytest_cmdopt_handle.
+    '''
+    assert os.path.exists(cmdopt)
+
+    print("run test cases in:")
+    print(cmdopt)
+
+if __name__ == "__main__":
+    pytest.main()

samples/subsys/testsuite/pytest/src/main.c

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+/*
+ * Copyright (c) 2020 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <ztest.h>
+void test_pytest(void)
+{
+	TC_PRINT("Hello world\n");
+}
+
+void test_main(void)
+{
+	ztest_test_suite(test_pytest,
+			 ztest_unit_test(test_pytest)
+			 );
+
+	ztest_run_test_suite(test_pytest);
+}

samples/subsys/testsuite/pytest/testcase.yaml

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+tests:
+  sample.twister.pytest:
+    platform_allow: native_posix
+    harness: pytest
+    tags: testing pytest