rulebook-core/src/main/java/com/deliveredtechnologies/rulebook/StandardRule.java
@Override
  public Rule<T> when(Predicate<FactMap<T>> test) {
    _test = test;
    return this;
  }
@Override
  public Rule<T> when(Predicate<FactMap<T>> test) {
    _test = 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      the current object