This depends on what you mean by testing if an animation is "playing" or "not playing". An animation can be playing with an AnimationSpeed of 0 (set to zero or stopped using events).... Either way, if an image is displayed then an animation is playing. So, I think you're asking how to check if the frame rate for an animation is above zero. In which case, use something like:
System : Compare Two Values [Sprite.AnimationSpeed > 0]
To test if the sprite is on xxx animation:
System : Compare Two Values [Sprite.AnimationName = "xxx"]