### Question:
RoundBufferMultichannelSampleSource extends DoubleArraySampleSource implements OriginalMultichannelSampleSource, ChangeableMultichannelSampleSource { protected synchronized void incrNextInsertPos() { nextInsertPos++; if (nextInsertPos == sampleCount) { full = true; nextInsertPos = 0; } } RoundBufferMultichannelSampleSource(int channelCount, int sampleCount); DocumentView getDocumentView(); void setDocumentView(DocumentView documentView); @Override synchronized void addSampleChunk(float[] newSamples); @Override synchronized void addSamples(float[] newSamples); @Override synchronized void addSamples(List<float[]> newSamples); @Override synchronized void getSamples(int channel, double[] target, int signalOffset, int count, int arrayOffset); synchronized void getSamples(int channel, double[] target, int signalOffset, int count, int arrayOffset, boolean calibrate); @Override OriginalMultichannelSampleSource duplicate(); @Override void setCalibrationGain(float calibration); @Override void setChannelCount(int channelCount); @Override String getLabel(int channel); Object[] getLabels(); void setLabels(Object[] labels); @Override void lock(); @Override void unlock(); int getReceivedSampleCount(); @Override boolean isCalibrationCapable(); @Override float[] getCalibrationGain(); @Override boolean areIndividualChannelsCalibrationCapable(); @Override void setCalibrationGain(float[] calibration); @Override float getSingleCalibrationGain(); @Override float getSamplingFrequency(); @Override void setSamplingFrequency(float sampling); @Override float[] getCalibrationOffset(); @Override void setCalibrationOffset(float[] calibrationOffset); @Override void setCalibrationOffset(float calibrationOffset); @Override float getSingleCalibrationOffset(); @Override void addSignalChangeListener(PluginSignalChangeListener listener); @Override long getAddedSamplesCount();  }### Answer:
@Test public void testIncrNextInsertPos() { assertEquals(0, theSource.getNextInsertPos()); theSource.incrNextInsertPos(); assertEquals(1, theSource.getNextInsertPos()); theSource.setNextInsertPos(TEST_SAMPLE_COUNT - 2); theSource.incrNextInsertPos(); assertEquals(TEST_SAMPLE_COUNT - 1, theSource.getNextInsertPos()); theSource.incrNextInsertPos(); assertEquals(0, theSource.getNextInsertPos()); }