try using registerCompletionHandler

package.json

@@ -63,7 +63,6 @@
 		"@rollup/plugin-commonjs": "^25.0.7",
 		"@rollup/plugin-json": "^6.1.0",
 		"@rollup/plugin-node-resolve": "^15.2.3",
-		"@shopify/semaphore": "^3.0.2",
 		"@sindresorhus/is": "^6.2.0",
 		"@sindresorhus/tsconfig": "^5.0.0",
 		"@types/common-tags": "^1.8.4",
@@ -117,7 +116,6 @@
 			"--import=tsimp"
 		],
 		"environmentVariables": {
-			"concurrency": "25",
 			"TSIMP_DIAG": "ignore"
 		}
 	}

test/_utils.ts

@@ -1,8 +1,7 @@
-/* eslint-disable ava/no-ignored-test-files */
+
 import process from 'node:process';
 import {fileURLToPath} from 'node:url';
-import test from 'ava';
-import {Semaphore} from '@shopify/semaphore';
+import test, {registerCompletionHandler} from 'ava';
 import {
 	execa,
 	type ExecaChildProcess,
@@ -62,12 +61,12 @@ type VerifyCliMacroArguments = [{
 	};
 }, 'expected' | 'error'>];
 
-const semaphore = new Semaphore(Number(process.env['concurrency']) || 5);
+registerCompletionHandler(() => {
+	process.exit(0);
+});
 
 export const _verifyCli = (baseFixture = defaultFixture) => test.macro<VerifyCliMacroArguments>(
 	async (t, {fixture = baseFixture, args, execaOptions, expected, error}) => {
-		const permit = await semaphore.acquire();
-
 		const assertions = await t.try(async tt => {
 			const arguments_ = args ? args.split(' ') : [];
 			const {all: output, exitCode} = await spawnFixture(fixture, arguments_, {reject: false, all: true, ...execaOptions}) as ExecaReturnValue & {all: string};
@@ -97,6 +96,5 @@ export const _verifyCli = (baseFixture = defaultFixture) => test.macro<VerifyCli
 		});
 
 		assertions.commit({retainLogs: !assertions.passed});
-		await permit.release();
 	},
 );