I am thinking to test an IC which have +9V and -9V supplies. To obtain a -9V, i intend to reverse connect a +9V battery. What can be negative effects, if there is? Thank you so much.
What can be negative effects,
Was this a pun? You are looking for negative effects!
Figure 1. A +/- 9 V supply using two 9 V batteries.
I intend to reverse connect a +9V battery.
We would probably say that we will series connect the batteries connecting one positive to the next negative and not "reversing" them. The idea is to keep all the voltages pointing the same direction.
Otherwise your understanding is correct.
If you would like to go for a package solution existing, I would recommend using a DC/DC converter such as: TracoPower-TMR Series Datasheet. I have used this one for OP-Amp dual supplies and it works fine.
It allows the dual output setting, where you can convert your input voltage (9V) to a dual +- voltage. Of course the corresponding part shall be selected accordingly.