如何编写单元测试来检查复制构造函数是否与类属性同步？

Question

Recently we had a bug in our system that is caused by forgetting to assign a newly added class property in the copy constructor.

For example:

public class MyClass {

    private Long companyId;
    private Long classId;
    private Double value;   <=  newly added

    public MyClass(MyClass myClass) {
        this.setCompanyId(myClass.getCompanyId());
        this.setClassId(myClass.getClassId());
        this.setValue(myClass.getValue());   <= we forget this line
    }

I want to write a unit test that guarantees to catch the missing copy assignment when a new property is added. How should I proceed with this?

Answer 1

I'd do this with reflection.

• New up an instance of MyClass . (A)
• Through reflection, assign a value to every field. This can be accomplished with getClass().getDeclaredFields() .
• New up a blank instance of MyClass . (B)
• Run the copy constructor on A against B.
• Through reflection, determine if the fields in A are equal to B.

Answer 2

You can override equals() method and use code snippet like that:

MyClass a = new MyClass();
// set properties of a
MyClass b = new MyClass(a);
Assert.assertEquals(a, b); // check that a.equals(b) returns true