Fix test-helpers.d.mts

Author: jdalton

test/utils/test-helpers.d.mts

@@ -1,5 +1,14 @@
 /** @fileoverview TypeScript declaration for test-helpers.mjs module. */
 
+interface IsolatePackageOptions {
+  entryPoints?: string[]
+}
+
+interface IsolatePackageResult<T = unknown> {
+  pkgPath: string
+  modules?: T[]
+}
+
 interface MultiEntryTestResult<T = unknown> {
   pkgPath: string
   modules: T[]
@@ -9,6 +18,11 @@ interface TestResult {
   pkgPath: string
 }
 
+export declare function isolatePackage<T = unknown>(
+  packageOrPath: string,
+  options?: IsolatePackageOptions,
+): Promise<IsolatePackageResult<T>>
+
 export declare function setupMultiEntryTest<T = unknown>(
   sockRegPkgName: string,
   entryPoints: string[],