More tests to make sure the code is correct

These three extra tests make sure the corresponding code is correct. The test for `outsideRanges` tests a case that wasn't tested before (numbers inside the ranges).

The test for `substringBetweenMatches` ensures that the code does not pass from hardcoding the length of the search string (3 for red).

The test for `addProperty` makes the expected behavior clearer. It also confirms that the student is using the bracket notation instead of testing for `obj.newProp` which is wrong.