How do I run Intern against Edge Chromium?

Question

I'm trying to run Intern against Microsoft Edge Chromium (beta) on a Mac. I've tried the steps listed in https://github.com/theintern/intern/blob/master/docs/how_to.md#run-tests-with-microsoft-edge-chromium-locally but I get an error:

Unable to create new service: EdgeDriverService

How do I resolve that?

I added a config to intern.json:

"edge-chromium": {
    "description": "run against Microsoft Edge Chromium",
    "environments": [
        {
            "browserName": "MicrosoftEdge",
            "browserVersion": "insider preview"
        }
    ]
},

and then run via:

npx intern config=@edge-chromium

When that didn't work I tried to explicitly add the driver, along with the drivers for the other browsers I'm testing against:

"tunnelOptions": {
    "drivers": [
        "firefox",
        "internet explorer",
        "MicrosoftEdge",
        { "name": "MicrosoftEdgeChromium", "version": "78.0.276.20" },
        {"name": "chrome", "version": "76.0.3809.68" }
    ]
}

That didn't help though.

I'm on Mac Catalina, using the latest Intern and the beta version of Edge.

The full error is:

SessionNotCreatedException: [POST http://localhost:4444/wd/hub/session / {"desiredCapabilities":{"name":"intern","idle-timeout":60,"browserName":"MicrosoftEdge","browserVersion":"insider preview"}}] Unable to create new service: EdgeDriverService
Build info: version: '3.141.59', revision: 'e82be7d358', time: '2018-11-14T08:25:53'
System info: host: 'mac.local', ip: '...', os.name: 'Mac OS X', os.arch: 'x86_64', os.version: '10.15', java.version: '12.0.1'
Driver info: driver.version: unknown
  at Server.post @ node_modules/src/Server.ts:361:16