Python program's "main()" not run on invocation

Python program's "main()" not run on invocation

I'm new to learning Python and using Eclipse + PyDev. I can't seem to
figure out why my program isn't running.
Here is my code:
def main():
print("Testing")
test1 = float(input("Test1: "))
test2 = float(input("Test2: "))
test3 = float(input("Test3: "))
calculate_cost (test1, test2, test3)
def calculate_cost (test1, test2, test3):
print("Testing")
I am assuming I am missing something in one or both of the functions to
make this run properly.