Change initial comment & stick through eclipse ...
to sort out identation. Not yet altered any functionality.
refactor myGcd method ... Test Program output ...
Instead call it GreatestCommonDivisor and give a comment explaining
algorith used.

Still not changed any functionality!

Test Program output:

$ java -ea FractionTest
FractionTest tests verbose output:
Invalid fraction with denominator 0
ERROR FractionTest FAILS for test "That 1/0 should throw an exception".
test "That multiplying 1/2 by 3/5 gives 3/10" passes.
test "That 1/2 .equals 1/2" passes.
test "That 1/2 .equals 3/6" passes.
test "That -1/2 .equals 1/-2" passes.
test "That -1/-2 .equals 1/2" passes.
test "That 4/-8 does not .equals 1/2" passes.
Exception in thread "main" java.lang.AssertionError: FractionTest failed 1 tests
	at FractionTest.simpleAssertTests(FractionTest.java:68)
	at FractionTest.main(FractionTest.java:22)