Null hypothesis testing can be done in virtually any scientific experiment.
A null hypothesis example would be what your prediction is in a given experiment. For example, my daughter performed an experiment to test the null hypothesis in her project.
She had to find out if a plant that is kept in direct sunlight and covered with a plastic Ziploc bag could survive a week without giving it water.
The sample null hypothesis was no and that it would eventually die without being watered. However, the test of null hypothesis failed and an alternative hypothesis had to be considered because the plant survived and was actually thriving because of condensation that occurred inside of the bag that allowed the plant to receive adequate moisture without actually giving it more water.