PayCalculator.java

package payroll;

public class PayCalculator {
  private boolean isHourlyWorker;

  public PayCalculator(boolean hourlyWorker) {
    isHourlyWorker = hourlyWorker;
  }

  public double calculate(double hours, double rate) {
    if (hours < 0 || hours > 80) {
      throw new RuntimeException("Hours out of range: " + hours);
    }

    if (isHourlyWorker) {
      double overtime = Math.max(0, hours - 40);
      return hours * rate + overtime * rate * 0.5;
    } else {
      return hours * rate;
    }
  }
}

PayCalculatorTest.java

import org.junit.Test;
import payroll.PayCalculator;

import static org.junit.Assert.assertEquals;

public class PayCalculatorTest {
  private PayCalculator hourlyCalculator = new PayCalculator(true);
  private PayCalculator contractorCalculator = new PayCalculator(false);

  private void assertPay(double expectedPay, double actualPay) {
    assertEquals(expectedPay, actualPay, .001);
  }

  @Test
  public void ZeroHours_ShouldBeZero() throws Exception {
    assertPay(0.0, hourlyCalculator.calculate(0, 10));
    assertPay(0.0, contractorCalculator.calculate(0, 10));
  }

  @Test(expected = RuntimeException.class)
  public void LessThanZeroHours_ShouldThrow() throws Exception {
    hourlyCalculator.calculate(-1, 10);
  }

  @Test(expected = RuntimeException.class)
  public void MoreThan80Hours_ShouldThrow() throws Exception {
    hourlyCalculator.calculate(81, 10);
  }

  @Test
  public void FortyHours_StraightTime() throws Exception {
    assertPay(400.0, hourlyCalculator.calculate(40, 10));
    assertPay(400.0, contractorCalculator.calculate(40, 10));
  }

  @Test
  public void FiftyHoursHourly_TimeAndHalf() throws Exception {
    assertPay(550.0, hourlyCalculator.calculate(50, 10));
  }

  @Test
  public void FiftyHoursNonHourly_StraightTime() throws Exception {
    assertPay(500.0, contractorCalculator.calculate(50, 10));
  }
}