Prediction

Key way to test hypothesis and resulting theory is by prediction.
Example
Newton’s laws of motion allow us to predict how an object will behave in certain circumstances. First law states “Every object persists in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.” Ref: http://www.grc.nasa.gov/WWW/k- 12/airplane/newton.html
Make prediction and perform experiment – put pen on level table, do not touch it and it stays where it is – therefore the theory holds up.
Combining Newton’s three laws of motion and his law of gravity with Johannes Kelpar’s three laws of planetary motion and we can predict the orbits of planets.
Applying these same laws to something too small to see, e.g. an atom, or something travelling at speed of light and predictions are far less accurate.
If a theory works then doesn’t we conduct research to determine the boundaries for theories and what happens outside them.