java - JUnit 测试方向

Question

我正在尝试了解 Junit 测试，并阅读了示例和其他内容，但仍然发现很难理解如何测试以及测试什么。下面是带有我创建测试用例的方法的类(以及我的测试用例类)。

import java.util.Iterator;

/**
 * The Probability class understands the likelihood that something will happen.
 * <p>
 * (c) Copyright Fred George 2008. All right reserved. Adapted and used for
 * educational purposes with permission from Fred George.
 * </p>
 * 
 * @author Fred George
 */
public class Probability {
    /** Value of receiver. */
    private final double value;
    /** Cannot happen. */
    private static final double IMPOSSIBLE_VALUE = 0.0;
    /** Will happen. */
    private static final double CERTAIN_VALUE = 1.0;
    /** Instance that represents outcome that will happen. */
    public static final Probability CERTAIN = new Probability(CERTAIN_VALUE);

    /**
     * Answer a new instance of the receiver with the specified value as the
     * likelihood that it occurs.
     * 
     * @param valueAsFraction
     *            value between 0.0 and 1.0
     * @throws
     */
    public Probability(final double valueAsFraction) {
        if (valueAsFraction < IMPOSSIBLE_VALUE || valueAsFraction > CERTAIN_VALUE) {
            throw new IllegalArgumentException("Specified value of "
                    + valueAsFraction + " is not between 0.0 and 1.0");
        }
        value = valueAsFraction;
    }

    /**
     * Answer the liklihood that the receiver will occur and the specified other
     * Probability will occur.
     * 
     * @return "and" of receiver and other Probability
     * @param other
     *            Probability being and'ed to receiver
     */
    public final Probability and(final Probability other) {
        return new Probability(this.value * other.value);
    }

    /**
     * Answer the value of the receiver as a scaled double between 0.0
     * (impossible) to 1.0 (certain).
     * <p>
     * This method is modeled after those in Double, Integer, and the rest of
     * the wrapper classes.
     * 
     * @return value of receiver as double between 0.0 and 1.0
     */
    public final double doubleValue() {
        return value;
    }

    /**
     * Answer true if the receiver has the same value as the other (assuming
     * other is a Probability).
     * 
     * @return true if receiver's value equals other's value
     * @param other
     *            Object (assumed to be Probability) to compare
     */
    public final boolean equals(final Object other) {
        if (!(other instanceof Probability)) {
            return false;
        }
        return this.value == ((Probability) other).value;
    }

    /**
     * Answers with a hashcode for the receiver.
     * @return the hash
     */
    public final int hashCode() {
        return (new Double(this.value)).hashCode();
    }

    /**
     * Answer true if the combined likelihoods of the specified Collection of
     * Probabilities sums to certain (100%).
     * 
     * @return true if combined likelihoods is 100%
     * @param probabilities
     *            Collection of likelihoods to sum
     */
    public static final boolean isTotalCertain(final java.util.Collection probabilities) {
        double sum = 0;
        for (Iterator i = probabilities.iterator(); i.hasNext();) {
            sum += ((Probability) i.next()).value;
        }
        return sum == CERTAIN_VALUE;
    }

    /**
     * Answer the liklihood that the receiver will not occur.
     * 
     * @return "not" of receiver
     */
    public final Probability not() {
        return new Probability(CERTAIN_VALUE - value);
    }

    /**
     * Answer the liklihood that the receiver will occur or the specified other
     * Probability will occur, or both.
     * 
     * @return "or" of receiver and other Probability
     * @param other
     *            Probability being or'ed to receiver
     */
    public final Probability or(final Probability other) {
        return this.not().and(other.not()).not(); // DeMorgan's Law
    }

    /** Multiplier from double to percentage. */
    private static final int PERCENTAGE_MULTIPLIER = 100;

    /**
     * Answers a String representation of the receiver suitable for debugging.
     * 
     * @return String representation of the receiver
     */
    public final String toString() {
        int percentage = (int) (value * PERCENTAGE_MULTIPLIER);
        return percentage + "%";
    }
}

这是我对一些测试用例所做的尝试。我还没有全部尝试过，但我坚持使用“等于”方法。

package edu.psu.ist.probability;

import edu.psu.ist.decision.Decision;
import junit.framework.TestCase;
import junit.framework.*;

public class ProbabilityTest extends TestCase {
    private Probability p1;
    private Probability p2;
    private Probability p3;
    private Decision d1;


    protected void setUp() {
        p1 = new Probability(.6);
        p2 = new Probability(.7);
        p3 = new Probability(.6);
        d1 = new Decision("No decision made");
    }

    public void testHashCode() {
        fail("Not yet implemented");
    }

    public void testProbability() {
        assertEquals(p1.doubleValue(), .6);
        try{
            p1 = p3;
            //get here, bad
            fail("Should raise an IllegalArgumentException");
        }catch (IllegalArgumentException e){
            //good!
        }

    }

    public void testAnd() {
        assertEquals((p1.and(p2)).doubleValue(), .42);
    }

    public void testDoubleValue() {
        assertEquals(p1.doubleValue(), .6);
    }

    public void testEqualsObject() {
        assertEquals(p1, p3);
        //assertEquals(p1, p2);
        assertTrue(!p1.equals(p2));
        assertTrue(p1.equals(p3));


        /*Probability p1 = new Probability (.7);
        Probability p2 = new Probability (.6);
        Decision d1 = new Decision();
        boolean TRUE = p1.equals(p2);
        boolean FALSE = p1.equals(d1);

        try {
            p1.equals(p2);
            p1.equals(d1);
            p1.equals(null);
        } catch (NullPointerException ex){
            // exception should be thrown
        }
//      assertEquals("Return true if theses values are the same",p1.doubleValue(), p2.doubleValue());
//      assertEquals("Return false if not equal", p1.doubleValue(), d1.equals(p1.doubleValue()));
//      assertNotSame("Objects are not the same", p1, d1);
        */
    }

    public void testIsTotalCertain() {
        fail("Not yet implemented");
    }

    public void testNot() {
        fail("Not yet implemented");
    }

    public void testOr() {
        fail("Not yet implemented");
    }

    public void testToString() {
        fail("Not yet implemented");
    }

}

也许有人可以阐明一些观点，帮助我更清楚地理解这个过程。

Answer 1

你选择了一个有点毛茸茸的第一步，comparing floating point numbers可能是不直观的。您需要确保使用带有增量的assertXXX方法:

double x = 1.3;
double y = 13.0 / 10.0;
double acceptable_difference = 0.05;
assertEquals(x,y, acceptable_difference);

这应该返回 true，因为您不太可能使您的值匹配。

在编写测试时，只需考虑您想要确保的内容，小心测试边界条件，例如某个概率是否为 0。

说到浮点，我打赌你会发现 not 的用途，让你的值低于 0.0，如果有那么一点点的话。这是值得一看的事情。