start implementing & testing evaluate. Test Output->

-> Test output shows that some work needs to be done!
$ java -ea FractionCalculatorTest
FractionCalculator verbose output:
Exception in thread "main" java.lang.NullPointerException
	at FractionCalculatorTest.simpleTests(FractionCalculatorTest.java:28)
	at FractionCalculatorTest.main(FractionCalculatorTest.java:11)