Computer Science 2

1. What is the relationship between 100% code coverage in your unit tests and bugs?
2. What is regression testing and when should it be applied?

/**
 * Simple linear income tax calculator based on preset rates and threshold levels.
 * <p>
 * Note: Intentionally contains bugs to illustrate the importance of unit testing.
 * </p>
 * @author Hyrum D. Carroll
 * @version 0.3, 09/08/20
 */
public class TaxCalculator{
    private double tax;  // the amount of tax due

    // annual income in dollars
    private final double LEVEL_1_INCOME = 10_000.00;
    private final double LEVEL_2_INCOME = 50_000.00;
    private final double LEVEL_3_INCOME = 100_000.00;

    private final double TAX_RATE_1 = 0.10; // % of income
    private final double TAX_RATE_2 = 0.15; // % of income
    private final double TAX_RATE_3 = 0.20; // % of income
    private final double TAX_RATE_4 = 0.30; // % of income

    /**
     * No-argument constructor
     */
    public TaxCalculator( ){
	tax = 0.0;
    }

    /**
     * Calculates the amount of tax due
     * <p>
     * Calculations are as follows:
     <ul>
     <li>if income is less than $10,000, 10% of income</li>
     <li>if income is less than $50,000, 15% of income</li>
     <li>if income is less than $100,000, 20% of income</li>
     <li>otherwise, 30% of income</li>
     </ul>
     * </p>
     * @param income the amount of income in dollars (and cents)
     * @return the amount of tax due
     */
    public double getTax( double income ){
	if( income < LEVEL_1_INCOME ){
	    tax = income * TAX_RATE_1;
	}else if( income < LEVEL_2_INCOME ){
	    tax = income * TAX_RATE_2;
	}else if( income < LEVEL_2_INCOME ){
	    tax = income * TAX_RATE_3;
	}else{
	    tax = income * TAX_RATE_4;
	}
	tax = Math.round(tax * 100.0) / 100.0; // round to 2 decimal places
	return tax;
    }
}

/**
 * Stores a pair of whole numbers
 * <p>
 * Caution: Class intentionally has one or more errors (for pedagogical purposes)
 * </p>
 * @author Hyrum D. Carroll
 * @version 0.2, 09/08/20
 */
public class NumberPairs {
    /** first number */
    private int value1;

    /** second number */
    private int value2;

    /**
     * Set the first value
     * @param valueVal the number for the first value
     */
    public void setValue1( int valueVal ){
        value1 = valueVal;
    }

    /**
     * Set the first value
     * @param valueVal the number for the second value
     */
    public void setValue2( int valueVal ){
        value2 = valueVal;
    }

    /**
     * Accessor for first value
     * @return the first value
     */
    public int getValue1(){
        return value1;
    }

    /**
     * Accessor for second value
     * @return the second value
     */
    public int getValue2(){
        return value1;
    }

    /**
     * Calculate the average of the two values
     * @return the average of the two values
     */
    public int averagePairs(){
        return value1 + value2 / 2;
    }
}