@Override
		protected boolean matches(Object item, Description mismatchDescription) {
			FileSink fs = (FileSink) item;
			try {
				String contents = fs.getContents();
				mismatchDescription.appendValue(contents);
				return matcher.matches(contents);
			}
			catch (IOException e) {
				mismatchDescription.appendText("failed with an IOException: " + e.getMessage());
				return false;
			}
		}
A matcher on the String contents of the sink, that delegates to another (String) matcher.

<p>
Instances are to be constructed using
{@code org.springframework.xd.shell.command.fixtures.XDMatchers#hasContentsThat}.

@author Eric Bottard
spring-xd-test-fixtures/src/main/java/org/springframework/xd/test/fixtures/FileSink.java