AffectedRowsMustSame return error if both affected rows are not same.

CurrentTimeStrAsLog return time format as "[2006/01/02 15:06:02.886 +08:00]".

DirExists checks if a dir exists.

ErrorMustSame return error if both error not same.

FileExists checks if a file exists and is not a directory before we try using it to prevent further errors.

FormatTimeStrAsLog format given time as as "[2006/01/02 15:06:02.886 +08:00]".

Rd implement Intn.

RdRange rand between [min(n, m), max(n, m)).

WrapErrExactlyNotSame wraps with ErrExactlyNotSame.

ErrExactlyNotSame is used when we can ensure that the result of a/b tests aren't same.