I started gming not while ago and now have question regarding Corruption points.

The rules say that "Corruption points (CP) operate much like Insanity points, except they are gained through exposure to the Warp..."

A character may prevent gaining insanity if he successfully passes the Willpower test. Therefore, if corruption points are similar to insanity points, can the character pass the Willpower test and avoid gaining Corruption points?

I'm pretty sure you can't. You're reading too much into that sentence. It's just saying that corruption, like insanity, is a counter that ticks up and bad things happen as you get more of it.

To be honest, I'm not 100% familiar with where in the rules you can prevent gaining IPs just by passing a Willpower test. That may just be something situational for that particular source of IPs, as usually you get them as a result of particular event occouring, and any related tests are usually detailed there.

But definitely with cps, the wording is more to describe how they count up to 100, not so much they follow the exact same rules (in case this willpower test to bypass IPs actually exists).

To be honest, I'm not 100% familiar with where in the rules you can prevent gaining IPs just by passing a Willpower test. That may just be something situational for that particular source of IPs, as usually you get them as a result of particular event occouring, and any related tests are usually detailed there.

However, it seems that the character can not prevent Corruption, unless she is the Sister of Battle from Enemy Within. Am I right?

Realize there are also other sources of IPs than the 1d5 for failing a Fear test with 3 DoFs.

Generally speaking, whatever source of CPs your seeing will tell you exactly how you can (if at all) to avoid them. Indeed some sources of corruption may just happen.

If you're bringing up Sororitas, its worth pointing out Enemies Within does have a talent that reduces CP gains as well (I wanna say there is a talent in core that does something similar, but I may be thinking first edition).