How can I detect which network I'm connected to? I'm in a unit test and I would like to use different test addresses depending on which network I'm connected to, to keep test output limited to the network I'm actually connected to.

I know I can run validateaddress to figure it out, but how can I detect this directly?
getblockchaininfo should tell you which chain you're on. For instance, on the main chain, you should get something like: 

{
    "result": {
        "chain": "main",   &lt;======= This is what you want
        "blocks": 519338,
        "headers": 519338,
        "bestblockhash": "0000000000000000001822f09f1821deb6b3b74e36ea1de4e232e5c60fa30ed9",
        "difficulty": 3839316899029.672,
        "mediantime": 1524358671,
        "verificationprogress": 0.9999957624003699,
        "chainwork": "0000000000000000000000000000000000000000018fa8011b05ef506160c4ff",
        "pruned": false,
        "softforks": [
            {
                "id": "bip34",
                "version": 2,
                "reject": {
                    "status": true
                }
            },
            {
                "id": "bip66",
                "version": 3,
                "reject": {
                    "status": true
                }
            },
            {
                "id": "bip65",
                "version": 4,
                "reject": {
                    "status": true
                }
            }
        ],
        "bip9_softforks": {
            "csv": {
                "status": "active",
                "startTime": 1462060800,
                "timeout": 1493596800,
                "since": 419328
            },
            "segwit": {
                "status": "active",
                "startTime": 1479168000,
                "timeout": 1510704000,
                "since": 481824
            }
        }
    },
    "error": null,
    "id": null
}