[Java] PowerMock 单元测试 : mock private method

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繁中版

这篇文章说明如果 Mock private Method ，帮助你减化 unit test 范围，进而提升写测试的意愿与让测试码更好维护。

假如你想测试 class 中的 Method A ，而这个 Method A 分别又去 call Method B / C ，为了降低测试的范围，我们会希望 Mock Method B 和 C 的 return 值 (mock 是指模拟物件的行为)。

B / C 如果是 public 或是 protected method ，我们只要使用 mockito or spock 就能轻松做到 mock，困难的是如果想 mock 的对象是 private method ， private method 只有 object 自已可以 access ，其它 test framework 都没办法对 private method 下手，目前唯有 PowerMock ，它直接修改了 java class byte-code ，把 private 改成 public accessible，让测试码能直接操作 private method 。

Example

Method A 
 - Call private Method B
 - Call private Method C

powerMock 使用范例

我有一个 class App.java，其中 log 是 public ， logInternal 是我想 mock 的 private method

App.java

package com;
 
public class App {
 
    public App() {
 
    }
 
    public String log() {
        System.out.println("run log");
        return this.logInternal();
    }
 
    private String logInternal() {
        System.out.println("run logInternal");
        return "internal";
    }
 
}

class AppTest.java: 需要使用 PowerMock 中的 createPartialMock / expectPrivate / replay 这 3 个

AppTest.java

package com;
 
import org.junit.Test;
import org.junit.runner.RunWith;
import static org.junit.Assert.assertEquals;
 
import org.powermock.api.easymock.PowerMock;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
 
@RunWith(PowerMockRunner.class)
@PrepareForTest(App.class)
public class AppTest {
 
    @Test
    public void TestLog() {
        try {
            App app = PowerMock.createPartialMock(App.class, "logInternal");
            PowerMock.expectPrivate(app, "logInternal").andReturn("mock_result");
            PowerMock.replay(app);
            String ret = app.log();
            assertEquals("Result is " + ret, ret, "mock_result");
        } catch (Exception e) {
            e.printStackTrace();
        }
 
 
    }
}

pom.xml dependency

Example

<dependency>
            <groupId>org.powermock</groupId>
            <artifactId>powermock-module-junit4</artifactId>
            <version>2.0.9</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.powermock</groupId>
            <artifactId>powermock-api-mockito2</artifactId>
            <version>2.0.9</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.powermock</groupId>
            <artifactId>powermock-api-easymock</artifactId>
            <version>2.0.9</version>
            <scope>test</scope>
        </dependency>

build.gradle

使用 gradle 的话，build config 可以参考这份

Example

plugins {
    id "application"
    id "java"
}
 
application {
    mainClassName = 'com.App'
}
 
 
allprojects {
    repositories {
        mavenCentral()
    }
}
 
dependencies {
    def powerMockVersion="2.0.9"
    implementation (
        "org.powermock:powermock-module-junit4:${powerMockVersion}",
        "org.powermock:powermock-api-mockito2:${powerMockVersion}",
        "org.powermock:powermock-api-easymock:${powerMockVersion}"
    )
}

参考资料

网页好读版

This post was last modified by puritys 2022/01/16