One-Sample Log-Rank Test

How to perform a one-Sample Log-Rank Test in R and is there a better way to compare mortality in the treatment group with predicted mortality (for example with predicted mortality by Seattle heart failure model)?

The log-rank test makes a relative comparison of survival time distributions so there is no one-sample version of it. And note that it will be difficult to do a fully proper comparison of predicted vs. observed survival probabilities without taking into account imprecision in the original Seattle heart failure model estimates (e.g., confidence intervals for predicted probabilities).