I mean you must be able to communicate clearly a variety of technical and business concepts in such a way that your audience both understands and is satisfied with the information.
Just this past week, my team has had to produce the following:
- several status reports for a release that goes to support and manufacturing Monday
- logged bugs based on automated tests that failed
- a summary of all the issues with one area of our product, including bugs, ideas for improvement, and "gotchas" that are related to customer configurations
- an explanation for a client about why an Active Directory user that our system uses must have certain privileges
- a script and accompanying documentation to handle diagnosis and cleanup of machines left in a bad state by nightly tests ("handling" here is logging a bug with appropriate information and logs)
- written results of a log analysis of a third-party product that is a client to our product and was having some problems interfacing to us; this was sent to the support team of the third-party product
There's no way one person can write all of this on their own. Producing a report of what you're doing is an essential part of being a good tester. I don't care how good you are at doing things; if you can't effectively talk about them to a variety of audiences you are less effective.
So next time you're bringing a new person on to your team, think about their testing skills and their ability to integrate with your group. Just don't forget to consider their writing skills as well.