Scala set a config value for a particular test

I have a reference.conf file which specify a config value as

prop {
    type = 2
}

I have scala test class and have a number of test under it. I want this config value to remain same for all tests except for one test which requires it to be 3. What is the best way to load a different config value for one particular test? Right now the config values are automatically loaded because I extend ScalatestRouteTest.

So how can I make a config file (or string) specially for that test and load it by specifying it while loading a config