Either of these could mean different things, in different contexts:
- My job involves writing tests (creating software that tests computer system integrity)
- My job involves writing tests (creating exams that test children's writing ability)
- I have some writing tests today (you have to sit, or complete a test of your writing ability)
When you abbreviate something, as you propose to in a list of duties, the context has already been set. The reader should know that you are an engineer and, presuming you have included this on your resume because you are pursuing a new job in the same industry, the reader should understand the same terminology as you do.
If I understand your intended meaning correctly - that your job involves creating test software, then either of your suggestions seem like they would be equally understandable to an English language speaker, in context. However, as this may be industry terminology, you would be best consulting someone within the same industry. Terminology does not always mirror idiomatic English language.