code: void log(CallInfo callInfo, DeltaAssertion da) {
      if (isEnabled(Option.LOG_ASSERTIONS) ||
          (    ! da.passed() 
              && isEnabled(Option.LOG_ASSERTION_ERRORS) )) {
        log.write(callInfo, da);
      }
    }
docs: Log delta assertion.
  @param callInfo Call info.
  @param da Delta assertion.