Exploration of Automotive Software testing in compliance with ISO 26262 Standard

Introduction

An Automotive software test cycle consist of Unit test, Integration test and System/Functional test. If the software is supposed to be used in Automotive applications it must qualify Functional Safety Automotive Standard ISO 26262.

ASIL

As per Automotive Safety Integrity Level the softwares are classified as A, B, C and D levels. The higher the level the more rigorous the development must be. In general the cost of development increases ten-fold from one level to next, that is ASIL-B is 10 times expensive than ASIL-A, whereas ASIL-C is 100 times and ASIL-D is 1000 times ASIL-A.

Systems like airbags, anti-lock brakes, and power steering require an ASIL-D grade the highest rigor applied to safety assurance because the risks associated with their failure are the highest. On the other end of the safety spectrum, components like rear lights require only an ASIL-A grade. Head lights and brake lights generally would be ASIL-B while cruise control would generally be ASIL-C.

For more ASIL related information do check out : https://www.synopsys.com/automotive/what-is-asil.html#:~:text=Systems%20like%20airbags%2C%20anti%2Dlock,only%20an%20ASIL%2DA%20grade .

1.Unit test

Software unit testing is focused on demonastrating the software units fullfil their specification with static and dynamic testing - that is, testing by executing the software in a simulated environment.

The following methods of unit testing are specified in part-6 of ISO 26262 standard.

Values, ++ : Highly recommended, + : Recommended and o : No recommendation

Methods for deriveing test cases for unit test

To evaluate the completeness of test cases and to demonstrate that there is no unintended functionality, ISO 26262 recommends structural coverage test (also known as white box testing) the structural metrics coverage are as follows.

2.Integration test

Integration test is performed at software integration stage. At this stage, different software units are brought togeather to work as one system. Integration test verifies that the resulting system performs as intended.

The following menthods are planned, specified and executed in accordance with clause 9 of part-8 of ISO 26262 standard.

Values, ++ : Highly recommended, + : Recommended and o : No recommendation

Methods for deriveing test cases for Integration test is same as unit test

Since coverage metrics for unit testing became unwieldly as the integrated system grows, ISO 26262 identifies a more appropriate set of coverage metrics which are as follows.

3.System/Functional test

The objective of System/Functional testing is to verify that the software fullfills its safety requirements int the target environment.

As per the ISO 26262 standard, the test shall be performed under the follwing test conditions.

1a. HIL (Hardware-in-the-loop) test

HIL testing marks a very crucial form of functional testing. The ECU under test is connected to a test system which can interact through inputs and outputs as if it were an actual vehicle.

A HIL system lets us validate different test scenarios without causing any danger to the real world environment.

Phases of the fundamental test process and activities of the test planning and test analysis

Example of a test case definition for a system integration test using a test case specification template

Thanks for reading.

Regards,

Harish Raj R

Reference :

1. Software Quality Journal - https://link.springer.com/journal/11219
2. https://www.embitel.com/wp-content/uploads/ISO-26262-Automotive-Software-Testing.pdf