建造者模式Builder是一種常用的設(shè)計(jì)模式，用于構(gòu)建不同的產(chǎn)品類。
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";
    }
}

以下是一個(gè)調(diào)用的場(chǎng)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標(biāo)志性的鏈?zhǔn)椒椒ㄕ{(diào)用(Fluent API)。
不過(guò)它這個(gè)也給單元測(cè)試造成了一定的麻煩。 先看這個(gè)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");
    }
}

這個(gè)用例跑失敗了

image.png

失敗的癥狀是拋出了空指針異常，根本原因是沒有正確的測(cè)試樁可供使用，因?yàn)樵谡{(diào)用sayHello時(shí)，mock的builder沒有被成功匹配。
看來(lái)得根據(jù)代碼依次來(lái)進(jìn)行打樁。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");
    }

這回跑通過(guò)了

image.png

不過(guò)問題來(lái)了，為了能匹配測(cè)試樁，需要逐個(gè)對(duì)鏈?zhǔn)秸{(diào)用中的各個(gè)中間返回對(duì)象進(jìn)行打樁。如果只是像這個(gè)案例的話，也就算了，如果碰到更為復(fù)雜的鏈?zhǔn)椒椒ㄕ{(diào)用，打樁的代碼就會(huì)一大片。
還好Mockito從2.0開始為這個(gè)問題提供了一個(gè)優(yōu)雅的解決方法。
RETURNS_SELF(new TriesToReturnSelf())

來(lái)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");
    }
}

通過(guò) @Mock(answer = RETURNS_SELF) ，告訴Mockito來(lái)返回被mock的測(cè)試樁自身，這樣就能支持鏈?zhǔn)椒椒ㄕ{(diào)用了。
以下是三個(gè)用例的執(zhí)行結(jié)果：

image.png

感興趣的讀者可以參考Mockito的Answers枚舉類，了解各種返回類型。

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());
//
}

據(jù)說(shuō)RETURNS_DEEP_STUBS也有類似效果，感興趣的讀者可以親自試一試。

關(guān)--祝 ： 軟件測(cè)試那些事