All my tasks was development, last week our boss gave me a testing task, and I completed it.
He said that the developers will hate me if I keep reporting every expected/unexpected, small/big, normal/critical bugs , so that he sent me back to the development team.
I just wondering if I misunderstand the word "testing"!!?

Testing can mean a lot of things.

Do not test.

... Unit testing?
... Fuzzy testing?
... testing a workflow that can consist of multiple steps and can involve multiple modules?
... testing a UI that changes dynamically for glitches?
... testing based on a persona the accessibility and usability of the program?
... testing as in having a concrete bug and trying to pinpoint the time when the program regressed ? (eg bisecting)

When someone says you should test something, do yourself and the QA a favor - make an exact definition of what and how to test, how much time you are allowed to spend and most important - record your steps.