JUNIT and Java

package fileio;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

import java.util.Locale;
import java.util.logging.Level;
import java.util.logging.Logger;

public class FileIO {
    private static final Logger LOGGER = Logger.getLogger( 
            Thread.currentThread().getStackTrace()[0].getClassName() );
    
    /** FileOutputStream Descriptor */        
    private FileOutputStream fos = null;
    /** OS-FileName */
    final private String fileName ;
    public FileOutputStream getFileOutputStream() { return fos; }
    public String getFileName() { return fileName; }
    
    public static void main(String[] args) {
        String writeContent = "This is my Data which needs" +
	        " to be written into the file";
        String fileName = "C:/myfile.txt";
        //LOGGER.setLevel(Level.FINEST);
        //LOGGER.setLevel(Level.SEVERE);              
        LOGGER.setLevel(Level.INFO);                  // Setting current Logger Level
        
        Locale.setDefault(new Locale("en", "EN"));  // Change Logger Language to English 
        FileIO fileIO = new FileIO(fileName);
        fileIO.doIO(fileName, writeContent);
    }
       
    public FileIO(String fileName) {
        this.fileName = fileName;
        LOGGER.info("FileIO constructor for fileName: " + fileName);
    }
/**
 * Opens, writes and closes FileOutputStream fos.
 * 

 * If open was successfull both fileName and FileOutputStream Object are 
 * stored in the related class attributes fileName, fos  for later access
 * @param  fName         The fileName at OS Level
 * @param  writeContent  The message to be written to our FileOutputStream
 * @return true          If write was successfull else return false
 */    
    public boolean doIO(String fName,String writeContent) {
        try {
            openStream(fName);  // Got an excpetion if open failse
            int bytesWritten = writeToStream( writeContent);
            boolean ret = closeStream();
            String loggerString =  new StringBuilder("Byte written to File  ")
                    .append( this.fileName ).append(": " ).append(bytesWritten).toString();
            LOGGER.info(loggerString);
            return true;
       }
       catch ( IOException ioe) {
                // Only log the Exception Message - stacktrace should be printed by low level 
                // Exception handler. Close the stream when there is am Exception !
            LOGGER.log( Level.SEVERE, ioe.toString()  );
            return false;
        }
        finally{
            closeStream(); 
        }
    }
    
/**
 * Opens a FileOutputStream fos. 
 * 

 * If open was successfull both fileName and FileOutputStream Object are 
 * stored in the related class attributes fileName, fos  for later access
 * @param  fileName     The fileName at OS Level
 * @throws IOException  If stream can't be opened at OS level 
 * @return true         If Stream was opened sucessfully 
 */
    public boolean openStream (String fileName) throws IOException {
        String fName = fileName;
        FileOutputStream lfos;
        File file;
    
        try {
            if ( fName == null ) {
                throw new IOException("fileName can't be null");
            }
            //Specify the file path here
            file = new File(fileName);
            lfos = new FileOutputStream(file);

          /* This logic will check whether the file  exists or not. If the file 
           * is not found at the specified location it would createa new file */
            if (!file.exists()) {
                file.createNewFile();
            }
            this.fos =  lfos; // save the FileOutputStream Descriptor for later usage
            return true;
        } catch ( IOException ioe) {
            String errorMesg = "Error open File-Stream " + fileName;
            LOGGER.log( Level.SEVERE, ioe.toString(), ioe );
            this.fos = null;
            throw new IOException(errorMesg);
        }
    }
     
 /**
 * Writes a String Message to already opened FileOutputStream fos.  
 * 

 * Note: This methode will convert a potenial NullPointerExceptions tiggered 
 *                        by either message=null or FileOutputStream fos=null to an IOExeption. 
 * @param  message        The String to be written to the Stream Descriptor fos
 * @throws IOException    If stream is not already opened at OS level or If messsage is null 
 * @return byteCnt        The number of bytes written to our opened Stream 
 */
   public int writeToStream( String message) throws IOException {
        try {
            /*String content cannot be directly written into
             * a file. It needs to be converted into bytes
            */
            if (message == null ) {
                throw new IOException("Message should NOT be null ! ");
            }
                // don't need to check for null !
            if (!(fos instanceof FileOutputStream)) {
                throw new IOException("FileOutputStream fos should NOT be null ! ");
            }
            byte[] bytesArray = message.getBytes();
            int byteCnt = bytesArray.length;
            fos.write(bytesArray);
            fos.flush();
            String loggerString =  new StringBuilder("Successfully written " )
                    .append( byteCnt ).append(" Bytes to File: ").append(fileName).toString();
            LOGGER.info(loggerString);
            
            return byteCnt;
        } 
        catch (IOException ioe) {       
            String errorMesg = "Error writing to File: " + fileName + "\n  " + ioe.toString();
            LOGGER.log( Level.SEVERE, ioe.toString(), ioe );
            throw new IOException(errorMesg);
        } 
    }
 
 /**
 * Closes FileOutputStream fos. 
 * 

 * Note: Closing an alreday closed FileOutputStream will not throw any error
 *       Even we get an error during close operation closeStream() methode will only log an error
 *       without re-throwing the underlying Exception.
 * @return true       if Stream was closed successfully
 */
    public boolean closeStream() { 
	try { 
	    if (fos != null) {
		    fos.close();
	    }
        fos = null;
        return true;
    } 
	catch (IOException ioe) {     
        String errorMesg = "Error closing Stream " + fileName;
        LOGGER.log( Level.SEVERE, ioe.toString(), ioe );
        return false;
	    }
    }
}

    @AfterClass
    public static void tearDownClass() {
    }
    
    @Before
    public void setUp() {
         String fName = "c:/myFileTest";
        instance = new FileIO(fName);
    }
    
    @After
    public void tearDown() {
    }

    /**
     * Test of main method, of class FileIO.
     */
    @Test
    public void testMain() {
        System.out.println("-> Start Test main()");
        String[] args = null;
        FileIO.main(args);
        System.out.println("   Test main() OK");
    }

    /**
     * Test of openStream method, of class FileIO.
     */
    @Test
    public void testOpenStream() {
        System.out.println("-> Start Test openStream()");
        String fName = "c:/myFileTest";
        boolean result = false;
        // FileIO instance = new FileIO();
        boolean expResult = true;
        try {
            result = instance.openStream(fName);
        } catch ( IOException iex) {}
        
        assertTrue("Expected Test Result " + expResult +  " - Got: " +  result,  expResult==result);
        System.out.println("   Test openStream() OK!");
    }
    
       /*
        *  Open a Non-Existing File - Should fail with an IOException    
        */
    @Test (expected=IOException.class)
    public void testOpenStreamFailed() throws IOException{
        System.out.println("-> Start Test testOpenStreamFailed() - Fails with an IOException !");
        String fName = "X:/myFileTestFailed";
        boolean result = false;
        FileOutputStream expResult = null;
        result = instance.openStream(fName);
    }
    
    /**
     * Test of writeToStream method, of class FileIO.
     */
    @Test 
    public void testWriteToStream() {
        String fName = "c:/myFileTest";
        FileOutputStream fos;
        int bytesWritten = 0;
        System.out.println("-> Start Test writeToStream()");
        String message = "This is just a Test";
        int bytesToBeWritten = message.getBytes().length ;
        try {
            instance.openStream(fName);
            bytesWritten = instance.writeToStream(message);
        } catch ( IOException iex) {}
        assertTrue("Error::  Expected bytesToBeWritten: " +  bytesToBeWritten 
                + " - GOT bytesWritten " + bytesWritten ,bytesWritten == bytesToBeWritten );
        System.out.println("   Test writeToStream() OK! - bytesWritten: " + bytesWritten);

    }

    /*
        In this test we simulate a write to a Not initialized Stream Desriptor
        This Test should fail with an IOExecption     
    */
    @Test (expected=IOException.class)
    public void testWriteToStreamFailed() throws IOException {
        String fName = "c:/myFileTest";
        FileOutputStream fos = null;

        System.out.println("-> Start testWriteToStreamFailed() - Fails with IOException !");
        String message = "This is just a Test";
        int bytesToBeWritten = message.getBytes().length ;
        // instance.writeToStream should trigger an IOException
        int bytesWritten = instance.writeToStream( message);
    }
    
    /**
     * Test of closeStream method, of class FileIO.
     * We also test that closing a closed Stream doesn't throw any Exception lile in socket opes
     */
    @Test
    public void testCloseStream() {
        String fName = "c:/myFileTest";
        FileOutputStream fos = null;
        System.out.println("-> Start Test closeStream()");
        String message = "This is just a Test";
        boolean result = false;
         
        // FileIO instance = new FileIO();
        try {
            instance.openStream(fName);
            result = instance.closeStream();
          } catch ( IOException iex) {}
        assertTrue("Error: Expected true in first close !", result);
            // Now closing an alreay closed Stream
        result = instance.closeStream();
        assertTrue("Error: Expected true in 2.nd close !", result);
        System.out.println("   Test closeStream() - 2.nd Close OK No Exception !" +
            " - ret Status: " + result );
    }

    /**
     * Test of doIO method, of class FileIO.
     * Should Work and return true !
     */
    @Test
    public void testDoIO() {
        System.out.println("-> Start Test doIO()");
        String fName = "c:/myFileTest";
         String writeContent = "This is my Data which needs" +
	        " to be written into the file";
        //FileIO instance = new FileIO();
        boolean result = instance.doIO(fName,writeContent);
        assertTrue("Error: Expected true !", result);
        System.out.println("   Test doIO() OK - result " + result );
    }    
    
    /**
     * Test of doIO method, of class FileIO. 
     * This test is the most important ONE as we will test that a failed Write closes fos 
     * descriptor to avoid a resource leak. To test this does we issue an add. write after calling 
     * doIO(). This add write should fail indicating that fos descriptor was already closed
     * TestString : null
     *              -> doIO() should return false but close fos
     *              -> An addition Write Test using the closed fos shoud fail too   
     */

    @Test
    public void testDoIOFailed() throws IOException {
        System.out.println("-> Start Test testDoIOFailed() - Fails with an Assert !");
        String fName = "c:/myFileTest";
        String writeContent = null;
        //FileIO instance = new FileIO();
        boolean result = instance.doIO(fName,writeContent);
        assertFalse("Error: Expected false !", result);
            // As we can get the Stream closed status form FileOutputStream object we start a test
            // write. Note: 
            // After a failure the Stream should be closed - we expect the the next write to fail !
        writeContent = "This WRITE should NOT Work";
        int bytesToBeWritten = writeContent.getBytes().length;
        int bytesWritten = -1;
        try {
            bytesWritten = instance.writeToStream( writeContent);
        } catch ( IOException e) {}
        assertFalse("This Write should fail - as the FOS descpriptor should be closed before!", bytesToBeWritten == bytesWritten );
    }    
    
    /* 
        Writing a null Message should reurn an IOException and Not a java.lang.NullPointerException 
    */
    @Test
    public void testWriteFailed() throws IOException{
        String fName = "c:/myFileTest";
        FileOutputStream fd;
        String message = null;
        int bytesToBeWritten = -1;
        int bytesWritten = -1;
        System.out.println("-> Start Test testWriteFailed() - Catches IOException !");
       
        instance.openStream(fName);
        fd = instance.getFileOutputStream();
        assertTrue(fd instanceof FileOutputStream);
     
        try {
            bytesWritten = instance.writeToStream( message);
        } catch ( IOException iex) {} 
        
        //  This Test raises an java.io.IOException: Message should NOT be null at all -
        // > bytesWritten remain unchanged 
        assertTrue("Error::  Expected bytesToBeWritten: " +  bytesToBeWritten 
                + " - GOT bytesWritten " + bytesWritten ,bytesWritten == bytesToBeWritten );
 
        boolean closeResult = instance.closeStream();
        assertTrue("Error: Expected true !", closeResult);       
        System.out.println("   Test testWriteFailed()  OK "  );
    }    
}

-> Start Test writeToStream()
   Test writeToStream() OK! - bytesWritten: 19
-> Start testWriteToStreamFailed() - Fails with IOException !
-> Start Test doIO()
   Test doIO() OK - result true
-> Start Test main()
   Test main() OK
-> Start Test closeStream()
   Test closeStream() - 2.nd Close OK No Exception ! - ret Status: true
-> Start Test openStream()
   Test openStream() OK!
-> Start Test testDoIOFailed() - Fails with an Assert !
-> Start Test testWriteFailed() - Catches IOException !
   Test testWriteFailed()  OK 
-> Start Test testOpenStreamFailed() - Fails with an IOException !
Mär 30, 2018 1:52:42 PM fileio.FileIO 
INFORMATION: FileIO constructor for fileName: c:/myFileTest
Mär 30, 2018 1:52:42 PM fileio.FileIO writeToStream
INFORMATION: Successfully written 19 Bytes to File: c:/myFileTest
Mär 30, 2018 1:52:42 PM fileio.FileIO 
INFORMATION: FileIO constructor for fileName: c:/myFileTest
Mär 30, 2018 1:52:42 PM fileio.FileIO writeToStream
SCHWERWIEGEND: java.io.IOException: FileOutputStream fos should NOT be null ! 
java.io.IOException: FileOutputStream fos should NOT be null ! 
	at fileio.FileIO.writeToStream(FileIO.java:122)
	at fileio.FileIOTest.testWriteToStreamFailed(FileIOTest.java:114)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	...

Mär 30, 2018 1:52:42 PM fileio.FileIO 
INFORMATION: FileIO constructor for fileName: c:/myFileTest
Mär 30, 2018 1:52:42 PM fileio.FileIO writeToStream
INFORMATION: Successfully written 55 Bytes to File: c:/myFileTest
Mär 30, 2018 1:52:42 PM fileio.FileIO doIO
INFORMATION: Byte written to File  c:/myFileTest: 55
Mär 30, 2018 1:52:42 PM fileio.FileIO 
INFORMATION: FileIO constructor for fileName: c:/myFileTest
Mar 30, 2018 1:52:42 PM fileio.FileIO 
INFO: FileIO constructor for fileName: C:/myfile.txt
Mar 30, 2018 1:52:42 PM fileio.FileIO writeToStream
INFO: Successfully written 55 Bytes to File: C:/myfile.txt
Mar 30, 2018 1:52:42 PM fileio.FileIO doIO
INFO: Byte written to File  C:/myfile.txt: 55
Mar 30, 2018 1:52:42 PM fileio.FileIO 
INFO: FileIO constructor for fileName: c:/myFileTest
Mar 30, 2018 1:52:42 PM fileio.FileIO 
INFO: FileIO constructor for fileName: c:/myFileTest
Mar 30, 2018 1:52:42 PM fileio.FileIO 
INFO: FileIO constructor for fileName: c:/myFileTest
Mar 30, 2018 1:52:42 PM fileio.FileIO writeToStream
SEVERE: java.io.IOException: Message should NOT be null ! 
java.io.IOException: Message should NOT be null ! 
	at fileio.FileIO.writeToStream(FileIO.java:119)
	at fileio.FileIO.doIO(FileIO.java:51)
	at fileio.FileIOTest.testDoIOFailed(FileIOTest.java:173)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	...

Mar 30, 2018 1:52:42 PM fileio.FileIO doIO
SEVERE: java.io.IOException: Error writing to File: c:/myFileTest
  java.io.IOException: Message should NOT be null ! 
Mar 30, 2018 1:52:42 PM fileio.FileIO writeToStream
SEVERE: java.io.IOException: FileOutputStream fos should NOT be null ! 
java.io.IOException: FileOutputStream fos should NOT be null ! 
	at fileio.FileIO.writeToStream(FileIO.java:122)
	at fileio.FileIOTest.testDoIOFailed(FileIOTest.java:182)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	..

Mar 30, 2018 1:52:42 PM fileio.FileIO 
INFO: FileIO constructor for fileName: c:/myFileTest
Mar 30, 2018 1:52:42 PM fileio.FileIO writeToStream
SEVERE: java.io.IOException: Message should NOT be null ! 
java.io.IOException: Message should NOT be null ! 
	at fileio.FileIO.writeToStream(FileIO.java:119)
	at fileio.FileIOTest.testWriteFailed(FileIOTest.java:204)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	...

Mar 30, 2018 1:52:42 PM fileio.FileIO 
INFO: FileIO constructor for fileName: c:/myFileTest
Mar 30, 2018 1:52:42 PM fileio.FileIO openStream
SEVERE: java.io.FileNotFoundException: X:\myFileTestFailed (Das System kann den angegebenen Pfad nicht finden)
java.io.FileNotFoundException: X:\myFileTestFailed (Das System kann den angegebenen Pfad nicht finden)
	at java.io.FileOutputStream.open0(Native Method)
	at java.io.FileOutputStream.open(FileOutputStream.java:270)
	at java.io.FileOutputStream.(FileOutputStream.java:213)
	at java.io.FileOutputStream.(FileOutputStream.java:162)
	at fileio.FileIO.openStream(FileIO.java:87)
	at fileio.FileIOTest.testOpenStreamFailed(FileIOTest.java:77)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        ...