FileExtension { public String asFileSuffix() { return EXTENSION_SEPARATOR + extension; } @VisibleForTesting  FileExtension(String extension); static FileExtension of(String extension); String appendExtension(String filePath); String asFileSuffix(); String getExtension(); @Override final boolean equals(Object o); @Override final int hashCode(); static final FileExtension ZIP; }
@Test void asFileSuffixShouldReturnDotAndExtension() { FileExtension fileExtension = new FileExtension("tar.gz"); assertThat(fileExtension.asFileSuffix()) .isEqualTo(".tar.gz"); }