When we develop applications the most important thing we can do is to ship code as fast and bug-free as possible. Testing helps us achieve those goals. The number one concern for developers who do not unit test is that it takes too long. When you're first getting into utilizing unit testing in development, it may take longer than you're used to. However, the long-term benefits far outweigh that initial investment, especially if we test before we write our application code. This is known as Test-driven Development (TDD).
We need to write a JavaScript function called isPrimary.
This function's main purpose is to return true if a number is a primary number and false if it's not.