matching abs replace ugly regex... Test output...
...with a much cleaner function and use to detect "clear" and "quit" entry.
But "clear" and "quit" code not yet written.

...Test output looks fine:
$ java -ea FractionCalculatorTest
FractionTestCalculator tests verbose output:
test "Simple parsing and operation: input of '1/2 * 3/4' should give '3/8'. Actually '3/8' is output." passes.

test "Simple parsing and operation: input of '1/2 / 3/4' should give '2/3'. Actually '2/3' is output." passes.

test "Simple parsing and operation: input of ' 1/2   +  -1/4 ' should give '1/4'. Actually '1/4' is output." passes.

test "Simple parsing and operation: input of '1/2 - 3/4' should give '-1/4'. Actually '-1/4' is output." passes.

test "Whole numbers: input of '3 * 9' should give '27'. Actually '27' is output." passes.

test "Abs: input of '-3 * 2/3 aB' should give '2'. Actually '2' is output." passes.

test "Neg: input of '3/7 N' should give '-3/7'. Actually '-3/7' is output." passes.

test "Invalid input no space: input of '1/2+1/2' should produce an ERROR. Actually '
ERROR unrecognized input '1/2+1/2' cannot process this
	Resetting calculator to its initial state (no operator and 0 as value)' is output." passes.

test "Invalid input two operators : input of '1/2 + - 3/4' should produce an ERROR. Actually '
ERROR you have input two operators: + and -.
	Resetting calculator to its initial state (no operator and 0 as value)' is output." passes.

test "Entering an invalid fraction input of '1/0' should produce an ERROR. Actually '
ERROR you have specified a fraction 1/0 with a zero denominator.
	Resetting calculator to its initial state (no operator and 0 as value)' is output." passes.

test "Try to divide by zero '1/2 / 0/3' should produce an ERROR. Actually '
ERROR you cannot divide by zero.
	Resetting calculator to its initial state (no operator and 0 as value)' is output." passes.

FractionCalculatorTest: All tests pass