### Question:
DefaultExtractorInput implements ExtractorInput { @Override public long getPosition() { return position; } DefaultExtractorInput(DataSource dataSource, long position, long length); @Override int read(byte[] target, int offset, int length); @Override boolean readFully(byte[] target, int offset, int length, boolean allowEndOfInput); @Override void readFully(byte[] target, int offset, int length); @Override int skip(int length); @Override boolean skipFully(int length, boolean allowEndOfInput); @Override void skipFully(int length); @Override boolean peekFully(byte[] target, int offset, int length, boolean allowEndOfInput); @Override void peekFully(byte[] target, int offset, int length); @Override boolean advancePeekPosition(int length, boolean allowEndOfInput); @Override void advancePeekPosition(int length); @Override void resetPeekPosition(); @Override long getPeekPosition(); @Override long getPosition(); @Override long getLength(); @Override void setRetryPosition(long position, E e);  }### Answer:
@Test public void testInitialPosition() throws Exception { FakeDataSource testDataSource = buildDataSource(); DefaultExtractorInput input = new DefaultExtractorInput(testDataSource, 123, C.LENGTH_UNSET); assertThat(input.getPosition()).isEqualTo(123); }