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public class Logger {
    private static Logger logger = null;
    private String lastLog = "";

    private Logger() {
    }

    public static Logger getInstance() {
        if(logger == null) {
            synchronized (Logger.class) {
                if(logger == null) {
                    logger = new Logger();
                }
            }
        }
        return logger;
    }

    public void log(String log) {
        lastLog = log;
        System.out.println("Log: [" + log + "]");
    }

    public String getLastLog() {
        return lastLog;
    }
}

public final class SettingsFileEngine {
    private static SettingsFileEngine settingsFileEngineInstance = null;
    private String fileName  = "";

    private SettingsFileEngine() {
    }

    public static SettingsFileEngine getInstance() {
        if(settingsFileEngineInstance == null) {
            synchronized (SettingsFileEngine.class) {
                if (settingsFileEngineInstance == null) {
                    settingsFileEngineInstance = new SettingsFileEngine();
                }
            }
        }
        return settingsFileEngineInstance;
    }

    public String getFileName() {
        return fileName;
    }

    public void open(final String fileName) {
        this.fileName = fileName;
        System.out.println("Opening the settings file");
    }

    public void close() {
        this.fileName = "";
        System.out.println("Closing the settings file");
    }

    public boolean loadSettings() {
        System.out.println("Loadind settings from file");
        return true;
    }

    public boolean saveSettings() {
        System.out.println("Saving settings to file");
        return true;
    }
}
//JUnit Test
public class LoggerTestSuite {
    @Test
    public void getLastLog() {
        //Given
        Logger.getInstance().log("New looog");
        Logger.getInstance().log("2nd looog");
        Logger.getInstance().log("3nd looog");
        //When & Then
        Assert.assertEquals("3nd looog", Logger.getInstance().getLastLog());
    }
}

public class SettingsFileEngineTestSuite {
    private static SettingsFileEngine settingsFileEngine;

    @BeforeClass
    public static void openSettingsFile() {
        SettingsFileEngine.getInstance().open(("myapp.settings"));
    }

    @AfterClass
    public static void closeSettingsFile() {
        SettingsFileEngine.getInstance().close();
    }

    @Test
    public void testGetFileName() {
        //Given
        //When
        String fileName = SettingsFileEngine.getInstance().getFileName();
        System.out.println("Opened: " + fileName);
        //Then
        Assert.assertEquals("myapp.settings", fileName);
    }

    @Test
    public void testLoadSettings() {
        //Given
        //When
        boolean result = SettingsFileEngine.getInstance().loadSettings();
        //Then
        Assert.assertTrue(result);
    }

    @Test
    public void testSaveSettings() {
        //Given
        //When
        boolean result = SettingsFileEngine.getInstance().saveSettings();
        //Then
        Assert.assertTrue(result);
    }
}