看,Mockito如何搞定Builder模式的Fluent API

Antony

发布于 2020-12-02 10:22:14

1K0

发布于 2020-12-02 10:22:14

建造者模式Builder是一种常用的设计模式，用于构建不同的产品类。如有以下的Builder

package com.github.mockito.builder;
class Builder{
    private String name;
    private String address;
    public Builder setName(String name){
        this.name = name;
        return this;
    }
    public Builder setAddress(String address){
        this.address = address;
        return this;
    }
    public String sayHello(){
        return "hello";
    }
}

以下是一个调用的场景

package com.github.mockito.builder;

public class BuilderDemo {
    public Builder builder;
    public String sayHello(){
        return builder.setName("name").setAddress("address").sayHello();
    }
}

建造者模式引人注目的是它标志性的链式方法调用(Fluent API)。不过它这个也给单元测试造成了一定的麻烦。先看这个案例

package com.github.mockito.builder;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;

import static org.assertj.core.api.Assertions.assertThat;
import static org.mockito.Mockito.when;

public class BuilderDemoLegacyTest {
    @Mock
    Builder builder;

    @InjectMocks
    BuilderDemo builderDemo;

    @BeforeEach
    public void setUp() {
        MockitoAnnotations.initMocks(this);
    }
    @Test
    public void testSayHelloShouldFail() {
        when(builder.sayHello()).thenReturn("hi");
        assertThat(builderDemo.sayHello()).isEqualTo("hi");
    }
}

这个用例跑失败了

image.png

失败的症状是抛出了空指针异常，根本原因是没有正确的测试桩可供使用，因为在调用sayHello时，mock的builder没有被成功匹配。看来得根据代码依次来进行打桩。如下例，

    @Test
    public void testSayHelloLegacy() {
         when(builder.setName("name")).thenReturn(builder);
         when(builder.setAddress("address")).thenReturn(builder);
         when(builder.sayHello()).thenReturn("hi");
        assertThat(builderDemo.sayHello()).isEqualTo("hi");
    }

这回跑通过了

image.png

不过问题来了，为了能匹配测试桩，需要逐个对链式调用中的各个中间返回对象进行打桩。如果只是像这个案例的话，也就算了，如果碰到更为复杂的链式方法调用，打桩的代码就会一大片。还好Mockito从2.0开始为这个问题提供了一个优雅的解决方法。 RETURNS_SELF(new TriesToReturnSelf())

来看一下使用之后的案例

package com.github.mockito.builder;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.mockito.MockitoAnnotations;

import static org.assertj.core.api.Assertions.assertThat;
import static org.mockito.Answers.RETURNS_SELF;
import static org.mockito.Mockito.when;

public class BuilderDemoTest {
    @Mock(answer = RETURNS_SELF)
    Builder builder;

    @InjectMocks
    BuilderDemo builderDemo;

    @BeforeEach
    public void setUp() {
        MockitoAnnotations.initMocks(this);
    }

    @Test
    public void testSayHello() {
//         when(builder.setName("name")).thenReturn(builder);
//         when(builder.setAddress("address")).thenReturn(builder);
         when(builder.sayHello()).thenReturn("hi");
        assertThat(builderDemo.sayHello()).isEqualTo("hi");
    }
}

通过 @Mock(answer = RETURNS_SELF) ，告诉Mockito来返回被mock的测试桩自身，这样就能支持链式方法调用了。以下是三个用例的执行结果：

感兴趣的读者可以参考Mockito的Answers枚举类，了解各种返回类型。

package org.mockito;
//
public enum Answers implements Answer<Object> {
    RETURNS_DEFAULTS(new GloballyConfiguredAnswer()),
    RETURNS_SMART_NULLS(new ReturnsSmartNulls()),
    RETURNS_MOCKS(new ReturnsMocks()),
    RETURNS_DEEP_STUBS(new ReturnsDeepStubs()),
    CALLS_REAL_METHODS(new CallsRealMethods()),
    RETURNS_SELF(new TriesToReturnSelf());
//
}

据说RETURNS_DEEP_STUBS也有类似效果，感兴趣的读者可以亲自试一试。

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原始发表：2020-10-19，如有侵权请联系 cloudcommunity@tencent.com 删除

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