Updated the test system

test/toDecimalMark.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {toDecimalMark} = require('./_30s.js');
+
+test('toDecimalMark is a Function', () => {
+  expect(toDecimalMark).toBeInstanceOf(Function);
+});
+test('convert a float-point arithmetic to the Decimal mark form', () => {
+  expect(toDecimalMark(12305030388.9087)).toBe('12,305,030,388.909');
+});