【SC随笔】Java测试mutator方法的注意点

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HIT-SC-LAB2需要实现一个Graph接口和两个具体的类ConcreteVerticesGraph.java和ConcreteEdgesGraph.java
接口有抽象方法Set

 /** * Add, change, or remove a weighted directed edge in this graph. * If weight is nonzero, add an edge or update the weight of that edge; * vertices with the given labels are added to the graph if they do not * already exi * s zero, remove the edge if it exists (the graph is not * otherwise modified). * * @param source label of the source vertex * @param target label of the target vertex * @param weight nonnegative weight of the edge * @return the previous weight of the edge, or zero if there was no such * edge */
    public int set(L source, L target, int weight);

设置一条边(权重不能为负数)，返回这条边原来的权重，如果原本不存在则返回零。
一开始写的测试用例不合格，只比较了返回值

    @Test
    public void testSet(){ 
   
        Graph<String> instance = emptyInstance();
        assertEquals("add a edge that doesn't exist before",
                0, instance.set("v1","v2",1));
        assertEquals("add a edge that doesn't exist before",
                0, instance.set("v1","v3",2));
        assertEquals("add a edge that doesn't exist before",
                0, instance.set("v2","v3",3));
        assertEquals("add a edge that does exist before",
                1, instance.set("v1","v2",5));
        assertEquals("remove a edge",
                5, instance.set("v1","v2",0));
        assertEquals("add a edge the source and target of it didn't exist",
                0, instance.set("v4","v5",1));
    }

然而对于mutator方法，仅仅测试返回值是否符合预期是不完备的，mutator改变了对象，就需要用observor方法观察是否发生了预期改变。
将测试用例更改如下：

 @Test
public void testSet(){ 

Graph<String> instance = emptyInstance();
assertEquals("add a edge that doesn't exist before",
0, instance.set("v1","v2",1));
Map<String,Integer> expect = new HashMap<>();
expect.put("v2",1);
assertEquals(expect,instance.targets("v1"));
assertEquals("add a edge that doesn't exist before",
0, instance.set("v1","v3",2));
expect.put("v3",2);
assertEquals(expect,instance.targets("v1"));
assertEquals("add a edge that doesn't exist before",
0, instance.set("v2","v3",3));
Map<String,Integer> expect2 = new HashMap<>();
expect2.put("v1",2);
expect2.put("v2",3);
assertEquals(expect2,instance.sources("v3"));
assertEquals("add a edge that does exist before",
1, instance.set("v1","v2",5));
expect.put("v2",5);
assertEquals(expect,instance.targets("v1"));
assertEquals("remove a edge",
5, instance.set("v1","v2",0));
expect.remove("v2");
assertEquals(expect,instance.targets("v1"));
assertEquals("add a edge the source and target of it didn't exist",
0, instance.set("v4","v5",1));
Map<String,Integer> expect3 = new HashMap<>();
expect3.put("v5",1);
assertEquals(expect3,instance.targets("v4"));
Map<String,Integer> expect4 = new HashMap<>();
expect4.put("v4",1);
assertEquals(expect4,instance.sources("v5"));
}