From fed1125b0e5e6e03bd058cb421e9423ef0fb19f8 Mon Sep 17 00:00:00 2001
From: Bingjia Yang <95595902+YBJ0000@users.noreply.github.com>
Date: Mon, 18 May 2026 21:01:49 +1000
Subject: [PATCH] fix(expect): allow readonly arrays and sets in toBeOneOf (fix
 #10264) (#10374)

---
 packages/expect/src/types.ts    |  2 +-
 test/unit/test/expect.test-d.ts | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/packages/expect/src/types.ts b/packages/expect/src/types.ts
index c2716caa2..5a037085e 100644
--- a/packages/expect/src/types.ts
+++ b/packages/expect/src/types.ts
@@ -152,7 +152,7 @@ interface CustomMatcher {
    * expect('foo').toBeOneOf([expect.any(String)])
    * expect({ a: 1 }).toEqual({ a: expect.toBeOneOf(['1', '2', '3']) })
    */
-  toBeOneOf: <T>(sample: Array<T> | Set<T>) => any
+  toBeOneOf: <T>(sample: ReadonlyArray<T> | ReadonlySet<T>) => any
 }
 
 export interface AsymmetricMatchersContaining extends CustomMatcher {
diff --git a/test/unit/test/expect.test-d.ts b/test/unit/test/expect.test-d.ts
index 20e480bb9..a37559ba4 100644
--- a/test/unit/test/expect.test-d.ts
+++ b/test/unit/test/expect.test-d.ts
@@ -119,4 +119,24 @@ test('expect.* allows asymmetrict mattchers with different types', () => {
     expect(value).toMatchObject(value)
   }
   expectMany({ enabled: true, data: 'ok' })
+
+  // toBeOneOf accepts readonly arrays and sets
+  // https://github.com/vitest-dev/vitest/issues/10264
+  {
+    const allowed = ['A', 'B'] as const
+    expect('A').toBeOneOf(allowed)
+    expect('A').toEqual(expect.toBeOneOf(allowed))
+
+    const readonlyArray: ReadonlyArray<string> = ['A', 'B']
+    expect('A').toBeOneOf(readonlyArray)
+    expect('A').toEqual(expect.toBeOneOf(readonlyArray))
+
+    const readonlySet: ReadonlySet<string> = new Set(['A', 'B'])
+    expect('A').toBeOneOf(readonlySet)
+    expect('A').toEqual(expect.toBeOneOf(readonlySet))
+
+    // mutable arrays and sets still work
+    expect('A').toBeOneOf(['A', 'B'])
+    expect('A').toBeOneOf(new Set(['A', 'B']))
+  }
 })
-- 
2.51.2