What it the right Testing strategy in Agile Scrum Kanban teams?

The problem is:

The team , I am working in has 10 developers to 2 testers ratio which means we are going to churn out code more quickly than it is "Test" done.

So, What should be the right approach to track activities in such scenarios according to agile experts?

My fear is that soon the day will come , when there is a lot of stuff which will be called as "Done" in previous sprints (with no testing done) but when it actually comes to testing, there might be some potential defects.

How can I track the efforts seamlessly? Should testing be part of "Done Definition"? What are the pitfalls if it is not?

As per me, it is sort of 'Waterfall' as you are calling stories "Done" before it is actually functionally tested.