使用 mockito-inline MockedConstruction 来模拟 FileInputStream throws Could not initialize mocked construction

Question

我正在尝试摆脱PowerMock并将其替换为mockito-inline新功能Mocking object construction ，因为我无法重构旧源代码。

我拥有的测试类之一是 mocking FileInputStream ，测试中的 class FileViewer

import java.awt.Button;
import java.awt.Event;
import java.awt.Font;
import java.awt.TextArea;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class FileViewer extends java.awt.Frame {
    private static final long serialVersionUID = 1L;
    Button close;
    GUIListener fGuiListener;

    public FileViewer() {
        super();
        fGuiListener = new GUIListener();
        addWindowListener(fGuiListener);
    }

    public FileViewer(String filename) throws IOException {
        super("FileViewer: " + filename);
        fGuiListener = new GUIListener();
        addWindowListener(fGuiListener);
        File f = new File(filename);
        int size = (int) f.length();
        int bytes_read = 0;
        byte[] data = new byte[size];
        try (FileInputStream in = new FileInputStream(f)) {
            while (bytes_read < size)
                bytes_read += in.read(data, bytes_read, size - bytes_read);
        }
        TextArea ta = new TextArea(new String(data, 0), 24, 80);
        ta.setFont(new Font("Helvetica", Font.PLAIN, 12));
        ta.setEditable(false);
        this.add("Center", ta);
        close = new Button("Close");
        this.add("South", close);
        this.pack();
        this.show();
    }

    public boolean action(Event e, Object what) {
        if (e.target == close) {
            this.hide();
            this.dispose();
            return true;
        } else
            return false;
    }
}

使用 powermock 的原始单元测试是

import static org.mockito.ArgumentMatchers.any;
import static org.mockito.ArgumentMatchers.anyInt;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

import java.io.FileInputStream;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mockito;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PowerMockIgnore;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

@PowerMockIgnore({ "javax.management.*", "javax.security.*" })
@RunWith(PowerMockRunner.class)
@PrepareForTest({ FileViewer.class, FileInputStream.class, java.awt.Frame.class })

public class FileViewerTest {
    String dir = System.getProperty("user.dir");
    String fileName = "/testFiles/testRead.txt";

    FileInputStream mockStream = null;

    @Before
    public void setup() throws Exception {
        mockStream = Mockito.mock(FileInputStream.class);
        when(mockStream.read(any(byte[].class), anyInt(), anyInt())).thenReturn(2000);
        PowerMockito.whenNew(FileInputStream.class).withAnyArguments().thenReturn(mockStream);
    }

    @Test
    public void testFileViewer_wFilename() throws Exception {
        FileViewer spy = Mockito.spy(new FileViewer(dir + fileName));
        verify(mockStream, times(1)).close();
        spy.dispose();
    }

}

我尝试按照示例Mock Java Constructors With Mockito | 配置和示例并使用 MockedConstruction 创建一个新的单元测试，如下所示

import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

import java.io.File;
import java.io.FileInputStream;

import org.junit.Test;
import org.mockito.MockedConstruction;
import org.mockito.Mockito;

public class FileViewerMockitoTest {
    String dir = System.getProperty("user.dir");
    String fileName = "/testFiles/testRead.txt";

    @Test
    public void testFileViewerWithFilename() throws Exception {
        try (MockedConstruction<FileInputStream> mocked = Mockito.mockConstruction(FileInputStream.class,
                (mock, context) -> {
                    // further stubbings ...
                    when(mock.read(any(), any(), any())).thenReturn((int) new File(dir + fileName).length() + 1);
                })) {

            FileViewer cut = new FileViewer(dir + fileName);
            verify(mocked, times(1)).close();
            cut.dispose();
        }
    }

}

但我得到以下异常

org.mockito.exceptions.base.MockitoException: Could not initialize mocked construction
    at java.io.FileInputStream.<init>(FileInputStream.java)
    at sun.misc.URLClassPath$FileLoader$1.getInputStream(URLClassPath.java:1385)
    at sun.misc.Resource.cachedInputStream(Resource.java:77)
    at sun.misc.Resource.getByteBuffer(Resource.java:160)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:455)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
    at com.cds.nrd.xss.util.FileViewerMockitoTest.testFileViewerWithFilename(FileViewerMockitoTest.java:30)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
    at org.junit.vintage.engine.execution.RunnerExecutor.execute(RunnerExecutor.java:43)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
    at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
    at java.util.Iterator.forEachRemaining(Iterator.java:116)
    at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
    at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
    at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
    at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
    at org.junit.vintage.engine.VintageTestEngine.executeAllChildren(VintageTestEngine.java:82)
    at org.junit.vintage.engine.VintageTestEngine.execute(VintageTestEngine.java:73)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:229)
    at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:197)
    at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:211)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:191)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:137)
    at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:98)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:40)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:529)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:756)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:452)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:210)
Caused by: java.lang.NullPointerException
    at com.cds.nrd.xss.util.FileViewerMockitoTest.lambda$0(FileViewerMockitoTest.java:27)
    at org.mockito.internal.creation.bytebuddy.InlineByteBuddyMockMaker$InlineConstructionMockControl.lambda$enable$0(InlineByteBuddyMockMaker.java:710)
    at org.mockito.internal.creation.bytebuddy.InlineByteBuddyMockMaker.lambda$new$3(InlineByteBuddyMockMaker.java:272)
    at org.mockito.internal.creation.bytebuddy.MockMethodAdvice.handleConstruction(MockMethodAdvice.java:176)
    at org.mockito.internal.creation.bytebuddy.inject.MockMethodDispatcher.handleConstruction(MockMethodDispatcher.java:53)
    ... 57 more

关于异常原因或如何使其工作或任何替代方法的任何想法？

Answer 1

找到解决方案：

我们无法在 try-with-resource 中的 lambda function 的存根中设置 any() 参数（在您的情况下， when(mock.read(any(), any(), any()))在FileViewerMockitoTest中），这将导致mock.read(any(), any(), any())抛出一个 NPE：“could not unbox null”（不知道它是什么意思）。

只需将（全部）这些 arguments 替换为any(ArgClass.class)之类的东西，就可以解决 NPE 问题，因此可以解决Could not initialize mocked construction MockitoException问题。

（我是怎么找到问题的？通过提取lambda function作为方法，我们可以在debug环境下得到NPE的真实描述。）

（令我惊讶的是，除此问题外，inte.net 上没有其他信息。）