Using partial mocks for non public methods testing

namespace MockByExample.Calculators
{
    /// <summary>
    /// Determines the business <see cref="RuleType"/> from a given integer value
    /// </summary>
    public class BusinessRuleCalculator
    {
        /// <summary>
        /// Determines the business <see cref="RuleType"/> from
        /// a passed value
        /// </summary>
        /// <param name="value">Integer value to determine the business value from</param>
        /// <returns>
        /// Zero if value is zero,
        /// see <see cref="GetRuleForNegative"/> for a negative value, 
        /// see <see cref="GetRuleForPositive"/> for a positive value
        /// </returns>
        public  RuleType GetRule(int value)
        {
            if(value == 0) return RuleType.Zero;
            return value > 0
                       ? GetRuleForPositive(value)
                       : GetRuleForNegative(value);
        }

        /// <summary>
        /// Determines the business rule type for a negative value
        /// </summary>
        /// <param name="value">Negative value to determine the rule type</param>
        /// <returns>
        /// OverThreshold if the value is less than -10, 
        /// NegativeAnomaly if the value is between -6 and -8 (inclusive), 
        /// otherwise NegativeNormalCase
        /// </returns>
        protected virtual RuleType GetRuleForNegative(int value)
        {
            if(value < -10) return RuleType.OverThreshold;
            return value.IsBetween(-6, -8)
                ? RuleType.NegativeAnomaly
                : RuleType.NegativeNormalCase;
        }

        /// <summary>
        /// Determines the business rule type for a positive value
        /// </summary>
        /// <param name="value">Positive value to determine the rule type</param>
        /// <returns>
        /// OverThreshold if the value is greater than 10, 
        /// PositiveAnomaly if the value is between 3 and 5 (inclusive), 
        /// otherwise PositiveNormalCase
        /// </returns>
        protected virtual RuleType GetRuleForPositive(int value)
        {
            if(value > 10) return RuleType.OverThreshold;
            return value.IsBetween(3, 5) 
                ? RuleType.PositiveAnomaly 
                : RuleType.PositiveNormalCase;
        }
    }
}