测试驱动开发英制单位转换

// Length.java
import org.junit.Test;
import static org.hamcrest.core.Is.is;
import static org.junit.Assert.assertThat;
public class LengthTest {
    @Test
    public void should_1_inch_equal_to_1_inch() {
        Length inch = new Length(1, Unit.Inch);
        assertThat(inch, is(new Length(1, Unit.Inch)));
    }
    @Test
    public void should_1_foot_equal_to_12_inches() {
        assertThat(new Length(1, Unit.Foot), is(new Length(12, Unit.Inch)));
    }
    @Test
    public void should_1_yard_equals_to_3_feet() {
        assertThat(new Length(1, Unit.Yard), is(new Length(3, Unit.Foot)));
        assertThat(new Length(2, Unit.Yard), is(new Length(72, Unit.Inch)));
    }
}
// Unit.java
public class Unit {
    public static Unit Inch = new Unit(1);
    public static Unit Foot = new Unit(12);
    public static Unit Yard = new Unit(36);
    private int transitionRateToInches;
    private Unit(int transitionRateToInches) {
        this.transitionRateToInches = transitionRateToInches;
    }
    int getAmountInInches(int rawAmount) {
        return rawAmount * transitionRateToInches;
    }
}
// Length.java
public class Length {
    private int amountInInches;
    public Length(int rawAmount, Unit unit) {
        this.amountInInches = unit.getAmountInInches(rawAmount);
    }
    @Override
    public boolean equals(Object object) {
        Length another = (Length)object;
        return this.amountInInches == another.amountInInches;
    }
}