Do you have a consistent nighttime routine? This is extremely important, especially at this age. Doesn't matter what it is or how short or long. But it must be a process and consistent.
Secondly, EVEN SO, my daughter will every so often really get into a testing-the-boundaries mode. Sometimes of course, it is b/c of a legit reason. Sometimes not. The best way I've learned to handle that is ask my husband to get involved. She most certainly tests me more than him. So if I've already tried and she's still giving me a hard time, he'll put her back down. She may resist a little more or not at all but will certainly respond differently. Moreover, I have found that whether with the sleeping issue or any other, it's almost as if they take turns (yeah, some overlap) with the testing of otherwise firm boundaries and routines. But I'm pretty solid (we are) on these things and I will consistently push back (basically) and if I've remained firm, she will get past it in about a week, week and a half tops. If I've bended, even a little here and there, then it tips the scales and her testing will last longer. It's normal and psychologically healthy that they pusch and test... but it's our job to lay down clear and consistent expectations without anger or compromise. They will re-adjust AND be more secure as a result. In the meanwhile, it pulls on our hearts, psycholigically tortures us and tempts us to compromise all the time. But remember to think long term and to be strong, your baby needs that in order to grow into the healthiest person s/he can be. Best wishes, N.