Added random tests.

Keep in mind that values larger than +/-1e+13 can lead to problems, so don't use too large random values.

I deleted the namespace from the code but I don't know how to write random tests. Give me an example, please. Then I will add some random tests.

Some points:

• You may provide random tests to avoid cheating. If you want to, I can give you an example.

• You don't need to implement a namespace, therefore an implemented namespace may be confusing for beginners.