rulebook-core/src/main/java/com/deliveredtechnologies/rulebook/StandardDecision.java
@Override
  public Decision<T, U> when(Predicate<FactMap<T>> test) {
    _rule.when(test);
    return this;
  }
@Override
  public Decision<T, U> when(Predicate<FactMap<T>> test) {
    _rule.when(test);
    return this;
  }
The when() method accepts a {@link Predicate} that returns true or false based on Facts.
@param test  the condition(s) to be evaluated against the Facts
@return      true, if the then() statement(s) should be evaluated, otherwise false