diff --git a/test/runner/browserstack/browsers.js b/test/runner/browsers.js
similarity index 67%
rename from test/runner/browserstack/browsers.js
rename to test/runner/browsers.js
index 7b703ceb..1ddccdf7 100644
--- a/test/runner/browserstack/browsers.js
+++ b/test/runner/browsers.js
@@ -1,6 +1,11 @@
 import chalk from "chalk";
-import { getBrowserString } from "../lib/getBrowserString.js";
-import { createWorker, deleteWorker, getAvailableSessions } from "./api.js";
+import { getBrowserString } from "./lib/getBrowserString.js";
+import {
+	createWorker,
+	deleteWorker,
+	getAvailableSessions
+} from "./browserstack/api.js";
+import createDriver from "./selenium/createDriver.js";
 
 const workers = Object.create( null );
 
@@ -8,12 +13,13 @@ const workers = Object.create( null );
  * Keys are browser strings
  * Structure of a worker:
  * {
- * 	 debug: boolean, // Stops the worker from being cleaned up when finished
- *   id: string,
- *   lastTouch: number, // The last time a request was received
- *   url: string,
- *   browser: object, // The browser object
+ *   browser: object // The browser object
+ * 	 debug: boolean // Stops the worker from being cleaned up when finished
+ *   lastTouch: number // The last time a request was received
+ *   restarts: number // The number of times the worker has been restarted
  *   options: object // The options to create the worker
+ *   url: string // The URL the worker is on
+ *   quit: function // A function to stop the worker
  * }
  */
 
@@ -31,70 +37,8 @@ const RUN_WORKER_TIMEOUT = 60 * 1000 * 2;
 
 const WORKER_WAIT_TIME = 30000;
 
-export function touchBrowser( browser ) {
-	const fullBrowser = getBrowserString( browser );
-	const worker = workers[ fullBrowser ];
-	if ( worker ) {
-		worker.lastTouch = Date.now();
-	}
-}
-
-async function waitForAck( worker, { fullBrowser, verbose } ) {
-	delete worker.lastTouch;
-	return new Promise( ( resolve, reject ) => {
-		const interval = setInterval( () => {
-			if ( worker.lastTouch ) {
-				if ( verbose ) {
-					console.log( `\n${ fullBrowser } acknowledged.` );
-				}
-				clearTimeout( timeout );
-				clearInterval( interval );
-				resolve();
-			}
-		}, ACKNOWLEDGE_INTERVAL );
-
-		const timeout = setTimeout( () => {
-			clearInterval( interval );
-			reject(
-				new Error(
-					`${ fullBrowser } not acknowledged after ${
-						ACKNOWLEDGE_TIMEOUT / 1000 / 60
-					}min.`
-				)
-			);
-		}, ACKNOWLEDGE_TIMEOUT );
-	} );
-}
-
-async function restartWorker( worker ) {
-	await cleanupWorker( worker, worker.options );
-	await createBrowserWorker(
-		worker.url,
-		worker.browser,
-		worker.options,
-		worker.restarts + 1
-	);
-}
-
-export async function restartBrowser( browser ) {
-	const fullBrowser = getBrowserString( browser );
-	const worker = workers[ fullBrowser ];
-	if ( worker ) {
-		await restartWorker( worker );
-	}
-}
-
-async function ensureAcknowledged( worker ) {
-	const fullBrowser = getBrowserString( worker.browser );
-	const verbose = worker.options.verbose;
-	try {
-		await waitForAck( worker, { fullBrowser, verbose } );
-		return worker;
-	} catch ( error ) {
-		console.error( error.message );
-		await restartWorker( worker );
-	}
-}
+// Limit concurrency to 8 by default in selenium
+const MAX_SELENIUM_CONCURRENCY = 8;
 
 export async function createBrowserWorker( url, browser, options, restarts = 0 ) {
 	if ( restarts > MAX_WORKER_RESTARTS ) {
@@ -104,37 +48,51 @@ export async function createBrowserWorker( url, browser, options, restarts = 0 )
 			) }`
 		);
 	}
-	const verbose = options.verbose;
-	while ( ( await getAvailableSessions() ) <= 0 ) {
+	const { browserstack, debug, headless, runId, tunnelId, verbose } = options;
+	while ( await maxWorkersReached( options ) ) {
 		if ( verbose ) {
 			console.log( "\nWaiting for available sessions..." );
 		}
 		await new Promise( ( resolve ) => setTimeout( resolve, WORKER_WAIT_TIME ) );
 	}
 
-	const { debug, runId, tunnelId } = options;
 	const fullBrowser = getBrowserString( browser );
 
-	const worker = await createWorker( {
-		...browser,
-		url: encodeURI( url ),
-		project: "jquery-migrate",
-		build: `Run ${ runId }`,
-
-		// This is the maximum timeout allowed
-		// by BrowserStack. We do this because
-		// we control the timeout in the runner.
-		// See https://github.com/browserstack/api/blob/b324a6a5bc1b6052510d74e286b8e1c758c308a7/README.md#timeout300
-		timeout: 1800,
-
-		// Not documented in the API docs,
-		// but required to make local testing work.
-		// See https://www.browserstack.com/docs/automate/selenium/manage-multiple-connections#nodejs
-		"browserstack.local": true,
-		"browserstack.localIdentifier": tunnelId
-	} );
+	let worker;
+
+	if ( browserstack ) {
+		worker = await createWorker( {
+			...browser,
+			url: encodeURI( url ),
+			project: "jquery",
+			build: `Run ${ runId }`,
+
+			// This is the maximum timeout allowed
+			// by BrowserStack. We do this because
+			// we control the timeout in the runner.
+			// See https://github.com/browserstack/api/blob/b324a6a5bc1b6052510d74e286b8e1c758c308a7/README.md#timeout300
+			timeout: 1800,
+
+			// Not documented in the API docs,
+			// but required to make local testing work.
+			// See https://www.browserstack.com/docs/automate/selenium/manage-multiple-connections#nodejs
+			"browserstack.local": true,
+			"browserstack.localIdentifier": tunnelId
+		} );
+		worker.quit = () => deleteWorker( worker.id );
+	} else {
+		const driver = await createDriver( {
+			browserName: browser.browser,
+			headless,
+			url,
+			verbose
+		} );
+		worker = {
+			quit: () => driver.quit()
+		};
+	}
 
-	browser.debug = !!debug;
+	worker.debug = !!debug;
 	worker.url = url;
 	worker.browser = browser;
 	worker.restarts = restarts;
@@ -147,6 +105,14 @@ export async function createBrowserWorker( url, browser, options, restarts = 0 )
 	return ensureAcknowledged( worker );
 }
 
+export function touchBrowser( browser ) {
+	const fullBrowser = getBrowserString( browser );
+	const worker = workers[ fullBrowser ];
+	if ( worker ) {
+		worker.lastTouch = Date.now();
+	}
+}
+
 export async function setBrowserWorkerUrl( browser, url ) {
 	const fullBrowser = getBrowserString( browser );
 	const worker = workers[ fullBrowser ];
@@ -155,6 +121,14 @@ export async function setBrowserWorkerUrl( browser, url ) {
 	}
 }
 
+export async function restartBrowser( browser ) {
+	const fullBrowser = getBrowserString( browser );
+	const worker = workers[ fullBrowser ];
+	if ( worker ) {
+		await restartWorker( worker );
+	}
+}
+
 /**
  * Checks that all browsers have received
  * a response in the given amount of time.
@@ -176,27 +150,12 @@ export async function checkLastTouches() {
 	}
 }
 
-export async function cleanupWorker( worker, { verbose } ) {
-	for ( const [ fullBrowser, w ] of Object.entries( workers ) ) {
-		if ( w === worker ) {
-			delete workers[ fullBrowser ];
-			await deleteWorker( worker.id );
-			if ( verbose ) {
-				console.log( `\nStopped ${ fullBrowser }.` );
-			}
-			return;
-		}
-	}
-}
-
 export async function cleanupAllBrowsers( { verbose } ) {
 	const workersRemaining = Object.values( workers );
 	const numRemaining = workersRemaining.length;
 	if ( numRemaining ) {
 		try {
-			await Promise.all(
-				workersRemaining.map( ( worker ) => deleteWorker( worker.id ) )
-			);
+			await Promise.all( workersRemaining.map( ( worker ) => worker.quit() ) );
 			if ( verbose ) {
 				console.log(
 					`Stopped ${ numRemaining } browser${ numRemaining > 1 ? "s" : "" }.`
@@ -209,3 +168,75 @@ export async function cleanupAllBrowsers( { verbose } ) {
 		}
 	}
 }
+
+async function maxWorkersReached( {
+	browserstack,
+	concurrency = MAX_SELENIUM_CONCURRENCY
+} ) {
+	if ( browserstack ) {
+		return ( await getAvailableSessions() ) <= 0;
+	}
+	return workers.length >= concurrency;
+}
+
+async function waitForAck( worker, { fullBrowser, verbose } ) {
+	delete worker.lastTouch;
+	return new Promise( ( resolve, reject ) => {
+		const interval = setInterval( () => {
+			if ( worker.lastTouch ) {
+				if ( verbose ) {
+					console.log( `\n${ fullBrowser } acknowledged.` );
+				}
+				clearTimeout( timeout );
+				clearInterval( interval );
+				resolve();
+			}
+		}, ACKNOWLEDGE_INTERVAL );
+
+		const timeout = setTimeout( () => {
+			clearInterval( interval );
+			reject(
+				new Error(
+					`${ fullBrowser } not acknowledged after ${
+						ACKNOWLEDGE_TIMEOUT / 1000 / 60
+					}min.`
+				)
+			);
+		}, ACKNOWLEDGE_TIMEOUT );
+	} );
+}
+
+async function ensureAcknowledged( worker ) {
+	const fullBrowser = getBrowserString( worker.browser );
+	const verbose = worker.options.verbose;
+	try {
+		await waitForAck( worker, { fullBrowser, verbose } );
+		return worker;
+	} catch ( error ) {
+		console.error( error.message );
+		await restartWorker( worker );
+	}
+}
+
+async function cleanupWorker( worker, { verbose } ) {
+	for ( const [ fullBrowser, w ] of Object.entries( workers ) ) {
+		if ( w === worker ) {
+			delete workers[ fullBrowser ];
+			await worker.quit();
+			if ( verbose ) {
+				console.log( `\nStopped ${ fullBrowser }.` );
+			}
+			return;
+		}
+	}
+}
+
+async function restartWorker( worker ) {
+	await cleanupWorker( worker, worker.options );
+	await createBrowserWorker(
+		worker.url,
+		worker.browser,
+		worker.options,
+		worker.restarts + 1
+	);
+}
diff --git a/test/runner/command.js b/test/runner/command.js
index fccc324d..462dba6e 100644
--- a/test/runner/command.js
+++ b/test/runner/command.js
@@ -2,10 +2,10 @@ import yargs from "yargs/yargs";
 import { browsers } from "./flags/browsers.js";
 import { getPlan, listBrowsers, stopWorkers } from "./browserstack/api.js";
 import { buildBrowserFromString } from "./browserstack/buildBrowserFromString.js";
-import { modules } from "./modules.js";
+import { modules } from "./flags/modules.js";
 import { run } from "./run.js";
-import { jqueryMigrate } from "./jquery-migrate.js";
-import { jquery } from "./jquery.js";
+import { jqueryMigrate } from "./flags/jquery-migrate.js";
+import { jquery } from "./flags/jquery.js";
 
 const argv = yargs( process.argv.slice( 2 ) )
 	.version( false )
@@ -68,15 +68,23 @@ const argv = yargs( process.argv.slice( 2 ) )
 			"Leave the browser open for debugging. Cannot be used with --headless.",
 		conflicts: [ "headless" ]
 	} )
+	.option( "retries", {
+		alias: "r",
+		type: "number",
+		description: "Number of times to retry failed tests by refreshing the URL."
+	} )
+	.option( "hard-retries", {
+		type: "number",
+		description:
+			"Number of times to retry failed tests by restarting the worker. " +
+			"This is in addition to the normal retries " +
+			"and are only used when the normal retries are exhausted."
+	} )
 	.option( "verbose", {
 		alias: "v",
 		type: "boolean",
 		description: "Log additional information."
 	} )
-	.option( "run-id", {
-		type: "string",
-		description: "A unique identifier for this run."
-	} )
 	.option( "isolate", {
 		type: "boolean",
 		description: "Run each module by itself in the test page. This can extend testing time."
@@ -93,19 +101,9 @@ const argv = yargs( process.argv.slice( 2 ) )
 			"Otherwise, the --browser option will be used, " +
 			"with the latest version/device for that browser, on a matching OS."
 	} )
-	.option( "retries", {
-		alias: "r",
-		type: "number",
-		description: "Number of times to retry failed tests in BrowserStack.",
-		implies: [ "browserstack" ]
-	} )
-	.option( "hard-retries", {
-		type: "number",
-		description:
-			"Number of times to retry failed tests in BrowserStack " +
-			"by restarting the worker. This is in addition to the normal retries " +
-			"and are only used when the normal retries are exhausted.",
-		implies: [ "browserstack" ]
+	.option( "run-id", {
+		type: "string",
+		description: "A unique identifier for the run in BrowserStack."
 	} )
 	.option( "list-browsers", {
 		type: "string",
diff --git a/test/runner/jquery-migrate.js b/test/runner/flags/jquery-migrate.js
similarity index 100%
rename from test/runner/jquery-migrate.js
rename to test/runner/flags/jquery-migrate.js
diff --git a/test/runner/jquery.js b/test/runner/flags/jquery.js
similarity index 100%
rename from test/runner/jquery.js
rename to test/runner/flags/jquery.js
diff --git a/test/runner/modules.js b/test/runner/flags/modules.js
similarity index 100%
rename from test/runner/modules.js
rename to test/runner/flags/modules.js
diff --git a/test/runner/listeners.js b/test/runner/listeners.js
index cca2bbd6..61a98e7c 100644
--- a/test/runner/listeners.js
+++ b/test/runner/listeners.js
@@ -53,6 +53,17 @@
 					return nu;
 				}
 			}
+
+			// Serialize Symbols as string representations so they are
+			// sent over the wire after being stringified.
+			if ( typeof value === "symbol" ) {
+
+				// We can *describe* unique symbols, but note that their identity
+				// (e.g., `Symbol() !== Symbol()`) is lost
+				var ctor = Symbol.keyFor( value ) !== undefined ? "Symbol.for" : "Symbol";
+				return ctor + "(" + JSON.stringify( value.description ) + ")";
+			}
+
 			return value;
 		}
 		return derez( object );
diff --git a/test/runner/browserstack/queue.js b/test/runner/queue.js
similarity index 89%
rename from test/runner/browserstack/queue.js
rename to test/runner/queue.js
index 6d1c8d51..843d5672 100644
--- a/test/runner/browserstack/queue.js
+++ b/test/runner/queue.js
@@ -1,5 +1,5 @@
 import chalk from "chalk";
-import { getBrowserString } from "../lib/getBrowserString.js";
+import { getBrowserString } from "./lib/getBrowserString.js";
 import {
 	checkLastTouches,
 	createBrowserWorker,
@@ -45,7 +45,7 @@ export function retryTest( reportId, maxRetries ) {
 		test.retries++;
 		if ( test.retries <= maxRetries ) {
 			console.log(
-				`Retrying test ${ reportId } for ${ chalk.yellow(
+				`\nRetrying test ${ reportId } for ${ chalk.yellow(
 					test.options.modules.join( ", " )
 				) }...${ test.retries }`
 			);
@@ -63,7 +63,7 @@ export async function hardRetryTest( reportId, maxHardRetries ) {
 		test.hardRetries++;
 		if ( test.hardRetries <= maxHardRetries ) {
 			console.log(
-				`Hard retrying test ${ reportId } for ${ chalk.yellow(
+				`\nHard retrying test ${ reportId } for ${ chalk.yellow(
 					test.options.modules.join( ", " )
 				) }...${ test.hardRetries }`
 			);
@@ -74,7 +74,7 @@ export async function hardRetryTest( reportId, maxHardRetries ) {
 	return false;
 }
 
-export function addBrowserStackRun( url, browser, options ) {
+export function addRun( url, browser, options ) {
 	queue.push( {
 		browser,
 		fullBrowser: getBrowserString( browser ),
@@ -87,7 +87,7 @@ export function addBrowserStackRun( url, browser, options ) {
 	} );
 }
 
-export async function runAllBrowserStack() {
+export async function runAll() {
 	return new Promise( async( resolve, reject ) => {
 		while ( queue.length ) {
 			try {
diff --git a/test/runner/reporter.js b/test/runner/reporter.js
index f3942ce9..91cdd297 100644
--- a/test/runner/reporter.js
+++ b/test/runner/reporter.js
@@ -3,6 +3,18 @@ import { getBrowserString } from "./lib/getBrowserString.js";
 import { prettyMs } from "./lib/prettyMs.js";
 import * as Diff from "diff";
 
+function serializeForDiff( value ) {
+
+	// Use naive serialization for everything except types with confusable values
+	if ( typeof value === "string" ) {
+		return JSON.stringify( value );
+	}
+	if ( typeof value === "bigint" ) {
+		return `${ value }n`;
+	}
+	return `${ value }`;
+}
+
 export function reportTest( test, reportId, { browser, headless } ) {
 	if ( test.status === "passed" ) {
 
@@ -25,9 +37,16 @@ export function reportTest( test, reportId, { browser, headless } ) {
 				message += `\n${ error.message }`;
 			}
 			message += `\n${ chalk.gray( error.stack ) }`;
-			if ( "expected" in error && "actual" in error ) {
-				message += `\nexpected: ${ JSON.stringify( error.expected ) }`;
-				message += `\nactual: ${ JSON.stringify( error.actual ) }`;
+
+			// Show expected and actual values
+			// if either is defined and non-null.
+			// error.actual is set to null for failed
+			// assert.expect() assertions, so skip those as well.
+			// This should be fine because error.expected would
+			// have to also be null for this to be skipped.
+			if ( error.expected != null || error.actual != null ) {
+				message += `\nexpected: ${ chalk.red( JSON.stringify( error.expected ) ) }`;
+				message += `\nactual: ${ chalk.green( JSON.stringify( error.actual ) ) }`;
 				let diff;
 
 				if ( Array.isArray( error.expected ) && Array.isArray( error.actual ) ) {
@@ -43,7 +62,7 @@ export function reportTest( test, reportId, { browser, headless } ) {
 					diff = Diff.diffJson( error.expected, error.actual );
 				} else if (
 					typeof error.expected === "number" &&
-					typeof error.expected === "number"
+					typeof error.actual === "number"
 				) {
 
 					// Diff numbers directly
@@ -54,30 +73,35 @@ export function reportTest( test, reportId, { browser, headless } ) {
 						diff = [ { removed: true, value: `${ value }` } ];
 					}
 				} else if (
-					typeof error.expected === "boolean" &&
-					typeof error.actual === "boolean"
+					typeof error.expected === "string" &&
+					typeof error.actual === "string"
 				) {
 
-					// Show the actual boolean in red
-					diff = [ { removed: true, value: `${ error.actual }` } ];
+					// Diff the characters of strings
+					diff = Diff.diffChars( error.expected, error.actual );
 				} else {
 
-					// Diff everything else as characters
-					diff = Diff.diffChars( `${ error.expected }`, `${ error.actual }` );
+					// Diff everything else as words
+					diff = Diff.diffWords(
+						serializeForDiff( error.expected ),
+						serializeForDiff( error.actual )
+					);
 				}
 
-				message += "\n";
-				message += diff
-					.map( ( part ) => {
-						if ( part.added ) {
-							return chalk.green( part.value );
-						}
-						if ( part.removed ) {
-							return chalk.red( part.value );
-						}
-						return chalk.gray( part.value );
-					} )
-					.join( "" );
+				if ( diff ) {
+					message += "\n";
+					message += diff
+						.map( ( part ) => {
+							if ( part.added ) {
+								return chalk.green( part.value );
+							}
+							if ( part.removed ) {
+								return chalk.red( part.value );
+							}
+							return chalk.gray( part.value );
+						} )
+						.join( "" );
+				}
 			}
 		}
 	}
diff --git a/test/runner/run.js b/test/runner/run.js
index f3676e5d..69ef86bd 100644
--- a/test/runner/run.js
+++ b/test/runner/run.js
@@ -8,16 +8,15 @@ import { createTestServer } from "./createTestServer.js";
 import { buildTestUrl } from "./lib/buildTestUrl.js";
 import { generateHash, printModuleHashes } from "./lib/generateHash.js";
 import { getBrowserString } from "./lib/getBrowserString.js";
-import { modules as allModules } from "./modules.js";
-import { cleanupAllBrowsers, touchBrowser } from "./browserstack/browsers.js";
+import { modules as allModules } from "./flags/modules.js";
+import { cleanupAllBrowsers, touchBrowser } from "./browsers.js";
 import {
-	addBrowserStackRun,
+	addRun,
 	getNextBrowserTest,
 	hardRetryTest,
 	retryTest,
-	runAllBrowserStack
-} from "./browserstack/queue.js";
-import { addSeleniumRun, runAllSelenium } from "./selenium/queue.js";
+	runAll
+} from "./queue.js";
 
 const EXIT_HOOK_WAIT_TIMEOUT = 60 * 1000;
 
@@ -271,6 +270,8 @@ export async function run( {
 				} );
 
 				const options = {
+					browserstack,
+					concurrency,
 					debug,
 					headless,
 					jquery,
@@ -282,11 +283,7 @@ export async function run( {
 					verbose
 				};
 
-				if ( browserstack ) {
-					addBrowserStackRun( url, browser, options );
-				} else {
-					addSeleniumRun( url, browser, options );
-				}
+				addRun( url, browser, options );
 			}
 		}
 	}
@@ -303,11 +300,7 @@ export async function run( {
 
 	try {
 		console.log( `Starting Run ${ runId }...` );
-		if ( browserstack ) {
-			await runAllBrowserStack( { verbose } );
-		} else {
-			await runAllSelenium( { concurrency, verbose } );
-		}
+		await runAll();
 	} catch ( error ) {
 		console.error( error );
 		if ( !debug ) {
diff --git a/test/runner/selenium/createDriver.js b/test/runner/selenium/createDriver.js
index d1680b22..095c1221 100644
--- a/test/runner/selenium/createDriver.js
+++ b/test/runner/selenium/createDriver.js
@@ -7,7 +7,7 @@ import { browserSupportsHeadless } from "../lib/getBrowserString.js";
 // Set script timeout to 10min
 const DRIVER_SCRIPT_TIMEOUT = 1000 * 60 * 10;
 
-export default async function createDriver( { browserName, headless, verbose } ) {
+export default async function createDriver( { browserName, headless, url, verbose } ) {
 	const capabilities = Capabilities[ browserName ]();
 	const prefs = new logging.Preferences();
 	prefs.setLevel( logging.Type.BROWSER, logging.Level.ALL );
@@ -77,5 +77,8 @@ export default async function createDriver( { browserName, headless, verbose } )
 	// Increase script timeout to 10min
 	await driver.manage().setTimeouts( { script: DRIVER_SCRIPT_TIMEOUT } );
 
+	// Set the first URL for the browser
+	await driver.get( url );
+
 	return driver;
 }
diff --git a/test/runner/selenium/queue.js b/test/runner/selenium/queue.js
deleted file mode 100644
index 2d62f695..00000000
--- a/test/runner/selenium/queue.js
+++ /dev/null
@@ -1,66 +0,0 @@
-// Build a queue that runs both browsers and modules
-// in parallel when the length reaches the concurrency limit
-// and refills the queue when one promise resolves.
-
-import chalk from "chalk";
-import { getBrowserString } from "../lib/getBrowserString.js";
-import { runSelenium } from "./runSelenium.js";
-
-const promises = [];
-const queue = [];
-
-const SELENIUM_WAIT_TIME = 100;
-
-// Limit concurrency to 8 by default in selenium
-// BrowserStack defaults to the max allowed by the plan
-// More than this will log MaxListenersExceededWarning
-const MAX_CONCURRENCY = 8;
-
-export function addSeleniumRun( url, browser, options ) {
-	queue.push( { url, browser, options } );
-}
-
-export async function runAllSelenium( { concurrency = MAX_CONCURRENCY, verbose } ) {
-	while ( queue.length ) {
-		const next = queue.shift();
-		const { url, browser, options } = next;
-
-		const fullBrowser = getBrowserString( browser, options.headless );
-		console.log(
-			`\nRunning ${ chalk.yellow( options.modules.join( ", " ) ) } tests ` +
-				`for jQuery Migrate ${ chalk.yellow( options.jqueryMigrate ) } ` +
-				`and jQuery ${ chalk.yellow( options.jquery ) } ` +
-				`in ${ chalk.yellow( fullBrowser ) } (${ chalk.bold( options.reportId ) })...`
-		);
-
-		// Wait enough time between requests
-		// to give concurrency a chance to update.
-		// In selenium, this helps avoid undici connect timeout errors.
-		await new Promise( ( resolve ) => setTimeout( resolve, SELENIUM_WAIT_TIME ) );
-
-		if ( verbose ) {
-			console.log( `\nTests remaining: ${ queue.length + 1 }.` );
-		}
-
-		const promise = runSelenium( url, browser, options );
-
-		// Remove the promise from the list when it resolves
-		promise.then( () => {
-			const index = promises.indexOf( promise );
-			if ( index !== -1 ) {
-				promises.splice( index, 1 );
-			}
-		} );
-
-		// Add the promise to the list
-		promises.push( promise );
-
-		// Wait until at least one promise resolves
-		// if we've reached the concurrency limit
-		if ( promises.length >= concurrency ) {
-			await Promise.any( promises );
-		}
-	}
-
-	await Promise.all( promises );
-}
diff --git a/test/runner/selenium/runSelenium.js b/test/runner/selenium/runSelenium.js
deleted file mode 100644
index 848db36c..00000000
--- a/test/runner/selenium/runSelenium.js
+++ /dev/null
@@ -1,30 +0,0 @@
-import createDriver from "./createDriver.js";
-
-export async function runSelenium(
-	url,
-	{ browser },
-	{ debug, headless, verbose } = {}
-) {
-	if ( debug && headless ) {
-		throw new Error( "Cannot debug in headless mode." );
-	}
-
-	const driver = await createDriver( {
-		browserName: browser,
-		headless,
-		verbose
-	} );
-
-	try {
-		await driver.get( url );
-		await driver.executeScript(
-`return new Promise( ( resolve ) => {
-	QUnit.on( "runEnd", resolve );
-} )`
-		);
-	} finally {
-		if ( !debug || headless ) {
-			await driver.quit();
-		}
-	}
-}