The rounding of a floating-point number to an integer or to a particular precision has to be done properly. The most common error is to cast the floating-point type float64 to an integer type and consider it as well-handled.
An example could be casting the number 3.9999 to an integer and expect it to become an integer of value 4. The real result would be 3. At the time of writing this book, the current version of Go (1.9.2) does not contain the Round function. However, in version 1.10, the Round function was already implemented in the math package.