Use of 'internal' in C# for Unit Testing

I'm learning C# for my new job and there seem to be an over-abundance of reserved words to use. One I came across is internal vs private. Where internal is similar to private, but the scope is in the assembly. I found this to be a bit silly, but then I came across a use that makes perfect sense to me. Creating APIs to access private variables for unit testing. To me, this is a great idea because there are often times that I would like to test internal items in isolation, but do not want to make APIs for others to use.