Here is the list of files in the Calculator Package $-$

$.$

$$ src

$$ Calculator

$$ Calculator.java

$$ test

$$ Calculator

$$ CalculatorTest.java

Calculator.Calculator class is fully implemented and contains a list of methods for each basic arithmetic operation. The only method that is different from what you$$d expect is divide$(),$ which throws an exception if someone tries to divide by zero.

This is interesting because when you write tests you will have to make sure your test tests the fact that exceptions are being thrown when expected and not being thrown when not expected.

Calculator.CalculatorTest class inside test$/$Calculator$/$CalculatorTest$.$java is empty. Let$$s talk about how to start writing this class.

In order to be able to write tests, you need to import a bunch of methods called assertions from a library called Junit. Here are some example assert methods $-$

assertEquals: takes two arguements, and checks if they are equal. If unequal, the test fails.

assertThrows: takes two arguements, the first being a class, and the second being a lambda expression.

You can get the class of an exception by using Exception.class, for example ArithmeticException.class or java.lang.ArithmeticException.class if you$$ve not imported it$.$

The lambda expression should include the method call that should throw an exception. You can think of it as a small convinient try block, for example $-$