Everybody has strengths and weaknesses. You are likely to be working in a job that suits your strengths, however that doesn’t mean you won’t be required to test something that seriously challenges your weaknesses. Weaknesses tend to fall into the acceptable and the unacceptable categories. Categories that subtly change depending on your company. Maybe when you’re with friends it’s unacceptable not to be able to name all the Number 1 hits from the music charts in the 90s. A skill that is unlikely to matter at work.
Unacceptable weaknesses are more of a challenge. People take it as a given that you can spot a bug in spelling or grammar but very few job interviews test for this.
I once tested a Polish language system. I don’t speak a word of Polish but this was an acceptable weakness. The testing role I was performing didn’t require me to actually read Polish, I was a functional tester in a team which also had a native Polish speaker to test the copy. Don’t be mistaken into thinking that my testing didn’t involve checking any of the system text. I couldn’t read the text but by deliberately ignoring it, thinking that it wasn’t my job, I would have perhaps missed several places where English had been mistakenly used instead of Polish. Maybe I would have even missed the screen layout problems caused by words being longer, or breaking in different places, to English.
The same system required me to test a financial product through its complete life-cycle. My background is not in financial services and so I hit upon an unacceptable weakness. Only by reading up on the financial product, and by talking to experts in the company could I gain enough understanding to be confident in testing the system. My lack of knowledge required that far more time and effort was expended to make sure all test plans were accurate. Exploratory testing was useful for trying to break the system but I was lacking the knowledge to allow me to test the system functionality without a scripted test plan.
Not all weaknesses are as obvious as this one. Consider for a moment how competent you believe you are in usability testing of websites. Most people consider themselves to have a reasonably good understanding of what makes a website easy and enjoyable to use. However there is a fascinating cognitive bias called The Dunning-Kruger Effect which states that incompetent people overestimate their abilities whereas competent people underestimate theirs. The great challenge is correctly identifying which side you stand on. It seems plausible that someone who hasn’t studied the complexities of usability will consider the problem to be far simpler than a UX expert who knows the subject in-depth.
The Dunning-Kruger Effect makes identifying weaknesses problematic. It is likely that if you are truly weak at an area then you will overestimate your abilities. You’ll be testing using knowledge that you don’t have. On the flip side you might be more competent that you realise but the Dunning-Kruger Effect will have you underestimating you abilities and probably conceding to ‘experts’ when in fact you should be challenging their opinions.
Either way you’re likely to be testing with an incomplete set of information.
So what can you do? The easy answer is to be aware. Question your assumptions and those of people around you. Always ask questions no matter how certain you are of the answer.
The hard answer is to address those (perceived) weaknesses. Get some training, read some books, do whatever it takes to learn enough about the subject to allow you to question subject experts, and ultimately software, with confidence.