Slow down.
Think.
The variable testVar has to retain its value from one iteration of loop() to the next.
Two ways of doing that:
- make it global.
- make it static within loop().
In either case, it will be initialised to zero automatically before setup() runs.
When one second is up, increment it.
Having incremented it, see if it is equal to 90.
If it is, do whatever you need to do.
If it isn't, wait for the next second.
Off you go.