Mocking a file, filewriter and csvwriter within a method for unit test throwing NullPointerException

Question

I'm trying to mock a file creation , FileWriter operation and CsvWriter operation. I'm using EasyMock to mock file creation , PowerMockito to mock FileWriter and CSVWriter operations. Even after mocking the file creation, junit showing NullPointerException..

My code is,

package example.mypackage.rms.utility;

import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import au.com.bytecode.opencsv.CSVWriter;

public class CSVBeanUtil {
    public static boolean writeToCsv(List<String[]> beanList, Path absPath) throws IOException {
        CSVWriter writer = new CSVWriter(new FileWriter(absPath.toAbsolutePath().toString()),
                CSVWriter.DEFAULT_SEPARATOR, CSVWriter.NO_QUOTE_CHARACTER);
        writer.writeAll(beanList);
        writer.close();
        return false;
    }

}

My Test Class is,

package example.mypackage.rms.unittest;

import static org.junit.Assert.assertEquals;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.util.ArrayList;
import java.util.List;
import example.mypackage.rms.config.AppConfig;
import example.mypackage.rms.entity.GiveUpFile;
import example.mypackage.rms.utility.CSVBeanUtil;
import org.easymock.EasyMock;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import org.powermock.modules.junit4.PowerMockRunnerDelegate;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.web.WebAppConfiguration;
import au.com.bytecode.opencsv.CSVWriter;

@WebAppConfiguration
@ContextConfiguration(classes = { AppConfig.class })
@PrepareForTest(CSVBeanUtil.class)
@RunWith(PowerMockRunner.class)
@PowerMockRunnerDelegate(SpringJUnit4ClassRunner.class)
public class UTCSVBeanUtil {
    @Test
    public void writeBeanToCsv() throws Exception {
        List<String[]> beanList = new ArrayList<String[]>();
        String[] st = new String[5];
        st[0] = "hai";
        beanList.add(st);
        final File fileMock = EasyMock.createMock(File.class);
        EasyMock.expect(fileMock.toPath()).andReturn(Paths.get("test.csv"));
        PowerMockito.mock(CSVWriter.class);
        PowerMockito.mock(FileWriter.class);
        PowerMockito.whenNew(FileWriter.class).withArguments(new File("test.csv")).thenReturn(null);
        PowerMockito.whenNew(CSVWriter.class)
                .withArguments(null, CSVWriter.DEFAULT_SEPARATOR, CSVWriter.NO_QUOTE_CHARACTER).thenReturn(null);

        /*
         * File createdFile= folder.newFile("myfile.csv");
         * ParseCsvToBean.writeBeanToCsv(beanList, "myfile.csv"); String s =
         * FileUtils.readFileToString(createdFile); //not working
         * assertEquals("hai", s);
         */

        /*
         * File createdFile= folder.newFile("myfile.csv");
         * FileUtils.writeStringToFile(createdFile, "hai"); String s =
         * FileUtils.readFileToString(createdFile); //working
         * assertEquals("hai", s);
         */
        boolean expected = false;
        boolean actual = CSVBeanUtil.writeToCsv(beanList, fileMock.toPath());
        assertEquals(expected, actual);

    }
}

And the exception is,

java.lang.NullPointerException at example.mypackage.rms.utility.CSVBeanUtil.writeToCsv(CSVBeanUtil.java:51) at example.mypackage.rms.unittest.UTCSVBeanUtil.writeBeanToCsv(UTCSVBeanUtil.java:114) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26) at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:73) at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:82) at org.junit.rules.ExternalResource$1.evaluate(ExternalResource.java:48) at org.junit.rules.RunRules.evaluate(RunRules.java:20) at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:73) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:224) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:83) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229) at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61) at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:68) at org.junit.runners.ParentRunner.run(ParentRunner.java:309) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:163) at org.powermock.modules.junit4.internal.impl.DelegatingPowerMockRunner$2.call(DelegatingPowerMockRunner.java:143) at org.powermock.modules.junit4.internal.impl.DelegatingPowerMockRunner$2.call(DelegatingPowerMockRunner.java:136) at org.powermock.modules.junit4.internal.impl.DelegatingPowerMockRunner.withContextClassLoader(DelegatingPowerMockRunner.java:127) at org.powermock.modules.junit4.internal.impl.DelegatingPowerMockRunner.run(DelegatingPowerMockRunner.java:136) at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:106) at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:53) at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:59) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

Please help me to solve this... Thank You...

Why for Pete's sake do you use a FileWriter from a Path? There is Files.newBufferedWriter() — fge
What do you actually test in that test? It looks to me like you have tested that your can write the method twice (the second time in an clunky way), but little else. Personally I'd just have a single integration test for this. — Michael Lloyd Lee mlk

Krzysztof Cichocki Krzysztof Cichocki · Accepted Answer · 2015-11-19T06:41:41

You create FileWriter with String:

new FileWriter(absPath.toAbsolutePath().toString())

But in test you expect a File():

 PowerMockito.whenNew(FileWriter.class).withArguments(new File("test.csv")).thenReturn(null);

Mocking a file, filewriter and csvwriter within a method for unit test throwing NullPointerException

2 Answers