private static Object convertArrayToCollectionIfNecessary(Object o) {
    if (isArray(o)) {
      return  GroovyRuntimeUtil.coerce(o, List.class);
    }
    return o;
  }
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