First, let's remember that hypothesis testing is an act in statistics whereby an analyst tests an assumption regarding a population parameter.
For example, you could choose the average dose of certain IV painkiller that causes adverse reactions, such as rashes, in patients over the age of 65.
Your hypothesis could be:
"Administering a dose of over 12mg of Oxycodone on patients over the age of 65 significantly increases their chances of developing complications"
And then you would proceed to test your hypothesis, to see if it is true.