@Nullable
    static MatcherCondition parse(Object target, String method, Object[] args, boolean safe) {
      if (safe) return null;

      if ("call".equals(method)) {
        if (args.length != 1 || !HamcrestFacade.isMatcher(args[0])) return null;
        return new MatcherCondition(target, args[0], true);
      }

      if ("that".equals(method) || "expect".equals(method)) {
        if (target != spock.util.matcher.HamcrestSupport.class) return null;
        if (args.length != 2 || !HamcrestFacade.isMatcher(args[1])) return null;
        return new MatcherCondition(args[0], args[1], false);
      }

      return null;
    }
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