private static String getComparisonString(final String str, final int index) {
        int start = index - 20;
        int end = index + 20;

        if (start < 0) {
            start = 0;
        }

        if (str.length() < end + 1) {
            end = str.length() - 1;
        }

        return str.substring(start, end);
    }
Generate a unified diff of the two files using the specified number of lines of context.
The diff output is sent to system out in coloured form.

@return True if the files are the same
stroom-test-common/src/main/java/stroom/test/common/ComparisonHelper.java