void replaceMatcherValues(List<Object> values) {
      boolean firstOccurrence = true;
      ListIterator<Object> iter = values.listIterator(values.size());

      while (iter.hasPrevious()) {
        Object value = iter.previous();
        if (!HamcrestFacade.isMatcher(value)) continue;

        if (firstOccurrence) {
          // indicate mismatch in condition output
          iter.set(shortSyntax ? false : ExpressionInfo.VALUE_NOT_AVAILABLE);
          firstOccurrence = false;
        } else {
          // don't show in condition output
          iter.set(ExpressionInfo.VALUE_NOT_AVAILABLE);
        }
      }
    }
A condition of the form "foo equalTo(bar)" or "that(foo, equalTo(bar)"
or "expect(foo, equalTo(bar)", where 'equalTo' returns a Hamcrest matcher.
spock-core/src/main/java/org/spockframework/runtime/SpockRuntime.java