When does "AssertionFailedError" error occur in ruby?

[Amit Bobade]

I am new to ruby. I am using Selenium with ruby. There is a condition where I am checking for the equality of the strings. When I am equating the strings with

 assert_equal(String1, String2)

Then it is showing error: AssertionFailed Error

So please tell me, when does "AssertionFaile dError" error occur in ruby?