My horse is very loving, thoughtful, and fun. But everyday she tries to see who is boss. Her actions vary and are small, but she is testing me. Talking low is usually all the discipline she needs. She is great and I love her dearly. Why does she test me and will she do this her entire life?
Horse have many natural instincts that were used as survival skills in the wild by their ancestors. Time will eventually eliminate the wild instincts from our horses, but not in our life time. So, yes your horse will always challenge you. You can minimize how often your horse does test you through training and encouraging a good attitude.

All horses have a natural pecking order that ranks them from the weakest to the strongest. Each ranking level will be challenged on a regular basis by a lower level horse. When you begin to work with your horse you will also be challenged to establish your ranking order. Your horse is not being disrespectful to you but as a safety measure he is seeking to insure the strongest mind is the leader. It is very important to show your horse through training programs and exercises that you are in full control and require him to do as you ask. This training should not be done at the time you are being challenged in a bad situation. Instead try achieving hierarchy when your horse's mind is capable of learning like in your arena. Your horse will show you more respect and love when you are the leader. You will never accomplish anything by łtip toeing˛ around your horse always accommodating and never reprimanding. You will find your horse respecting your stronger leadership.