如何为接口编写junit测试?

问题描述

为接口编写 junit 测试以便它们可用于具体实现类的最佳方法是什么?

What is the best way to write junit tests for interfaces so they can be used for the concrete implementing classes?

例如你有这个接口和实现类:

e.g. You have this interface and implementing classes:

public interface MyInterface {
    /** Return the given value. */
    public boolean myMethod(boolean retVal);
}

public class MyClass1 implements MyInterface {
    public boolean myMethod(boolean retVal) {
        return retVal;
    }
}

public class MyClass2 implements MyInterface {
    public boolean myMethod(boolean retVal) {
        return retVal;
    }
}

您将如何针对接口编写测试，以便将其用于类?

How would you write a test against the interface so you can use it for the class?

可能性 1:

public abstract class MyInterfaceTest {
    public abstract MyInterface createInstance();

    @Test
    public final void testMyMethod_True() {
        MyInterface instance = createInstance();
        assertTrue(instance.myMethod(true));
    }

    @Test
    public final void testMyMethod_False() {
        MyInterface instance = createInstance();
        assertFalse(instance.myMethod(false));
    }
}

public class MyClass1Test extends MyInterfaceTest {
    public MyInterface createInstance() {
        return new MyClass1();
    }
}

public class MyClass2Test extends MyInterfaceTest {
    public MyInterface createInstance() {
        return new MyClass2();
    }
}

专业:

• 只需要实现一种方法

缺点:

• 所有测试的被测类的依赖项和模拟对象必须相同

可能性 2:

public abstract class MyInterfaceTest
    public void testMyMethod_True(MyInterface instance) {
        assertTrue(instance.myMethod(true));
    }

    public void testMyMethod_False(MyInterface instance) {
        assertFalse(instance.myMethod(false));
    }
}

public class MyClass1Test extends MyInterfaceTest {
    @Test
    public void testMyMethod_True() {
        MyClass1 instance = new MyClass1();
        super.testMyMethod_True(instance);
    }

    @Test
    public void testMyMethod_False() {
        MyClass1 instance = new MyClass1();
        super.testMyMethod_False(instance);
    }
}

public class MyClass2Test extends MyInterfaceTest {
    @Test
    public void testMyMethod_True() {
        MyClass1 instance = new MyClass2();
        super.testMyMethod_True(instance);
    }

    @Test
    public void testMyMethod_False() {
        MyClass1 instance = new MyClass2();
        super.testMyMethod_False(instance);
    }
}

专业:

• 每个测试的精细粒度，包括依赖项和模拟对象

缺点:

• 每个实现测试类都需要编写额外的测试方法

您更喜欢哪种可能性或您使用什么其他方式?

Which possibility would you prefer or what other way do you use?

推荐答案

与@dlev 给出的投票率高的答案相反，有时像您建议的那样编写测试非常有用/很有必要.类的公共 API，如通过其接口所表达的，是最重要的要测试的东西.话虽如此，我不会使用您提到的任何一种方法，而是使用 参数化 改为 test，其中参数是要测试的实现:

Contrary to the much-voted-up answer that @dlev gave, it can sometimes be very useful/needful to write a test like you're suggesting. The public API of a class, as expressed through its interface, is the most important thing to test. That being said, I would use neither of the approaches you mentioned, but a Parameterized test instead, where the parameters are the implementations to be tested:

@RunWith(Parameterized.class)
public class InterfaceTesting {
    public MyInterface myInterface;

    public InterfaceTesting(MyInterface myInterface) {
        this.myInterface = myInterface;
    }

    @Test
    public final void testMyMethod_True() {
        assertTrue(myInterface.myMethod(true));
    }

    @Test
    public final void testMyMethod_False() {
        assertFalse(myInterface.myMethod(false));
    }

    @Parameterized.Parameters
    public static Collection<Object[]> instancesToTest() {
        return Arrays.asList(
                    new Object[]{new MyClass1()},
                    new Object[]{new MyClass2()}
        );
    }
}

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