According to the country where your product will be used, you have to refer to american or european standards for EMC and EC. For the others countries, I don't know which standards you have to follow.

If your products is part of a global system, you havn't to obtain any certification because this is the global system which has to be certified. However, it doesn't mean that you can do everything. Your product has still to be compliant with the standards.

The stantards gives all you need to design your product to be compliant. Note that there is a lot of standards according to your application (military, automotive, medical, industrial, agribusiness, ...).
For automotive application for example, you'll find specific standards for electrical, EMC, mechanical, signalling, packaging and so on...

When designing, this is the use to design according to the standards. But the final certification is not always given according to the tests conducted. You may not test a product if you're able to justify why (minor modification from an existing product, ...). In this case, you may obtain the certification from the documents you have to show at the Certification Office (In Europe, you have APAVE, CEPTEC, ....)

For heavy trucks applications, I can provide you the name of the standards used for US and Europe application. This covers the Electronic Control Units and it's giving a detailled idea of what are the constraints which you have to be compliant with.

If you need more, I could give you an example concerning the design for an Electronic Control Unit in truck application. I'll just give you the titles of each test made and the standards used.

Regards
Stephane