@Override
    public String toString() {
        StringBuilder string = new StringBuilder();
        string.append("condition '");
        string.append(conditionStr);
        string.append("'");
        if (requiredTimestamp != 0) {
            string.append(", required_timestamp ");
            string.append(Long.toUnsignedString(requiredTimestamp));
        }
        return string.toString();
    }
<p>Returns a TestAndSetCondition that requires the currently persisted document in the
backend to have a timestamp exactly matching the provided timestamp value.</p>

<p>Version compatibility note: older versions of Vespa that do not support timestamp
requirements as part of test and set conditions will observe a condition with only
a timestamp set as if the condition is <em>empty</em>, i.e. the operation will be
applied unconditionally.</p>

<p><strong>Note:</strong> this API is currently in Beta</p>

@param requiredTimestamp An (unsigned) timestamp corresponding exactly to the persisted
                         backend timestamp of the document to update.
document/src/main/java/com/yahoo/document/TestAndSetCondition.java