### Question:
B2FileContentSource implements B2ContentSource { @Override public String getSha1OrNull() throws IOException { return sha1OrNull; } private  B2FileContentSource(File source,
                                String sha1); static Builder builder(File source); static B2FileContentSource build(File source); @Override String getSha1OrNull(); @Override Long getSrcLastModifiedMillisOrNull(); @Override long getContentLength(); @Override InputStream createInputStream();  }### Answer:
@Test public void testGetSha1OrNull() throws IOException { assertNull(contentSource.getSha1OrNull()); final B2ContentSource withSha1 = B2FileContentSource .builder(file) .setSha1(SAMPLE_SHA1) .build(); assertEquals(SAMPLE_SHA1, withSha1.getSha1OrNull()); }