From 3e4f170bb69d09fa38ae6b2b301e726252a0ecf4 Mon Sep 17 00:00:00 2001
From: Rebecca Stevens <rebecca.stevens@outlook.co.nz>
Date: Sun, 9 Jan 2022 20:12:40 +1300
Subject: [PATCH] test(type-utils): add test for IndexSignature internals

---
 .../type-utils/tests/isTypeReadonly.test.ts   | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/packages/type-utils/tests/isTypeReadonly.test.ts b/packages/type-utils/tests/isTypeReadonly.test.ts
index d757c59869d1..751da80471f4 100644
--- a/packages/type-utils/tests/isTypeReadonly.test.ts
+++ b/packages/type-utils/tests/isTypeReadonly.test.ts
@@ -177,5 +177,31 @@ describe('isTypeReadonly', () => {
         });
       });
     });
+
+    describe('IndexSignature', () => {
+      describe('is readonly', () => {
+        it('handles readonly PropertySignature inside a readonly IndexSignature', () => {
+          const { type, checker } = getType(
+            `type Test = { readonly [key: string]: { readonly foo: readonly string[]; }; };`,
+          );
+
+          const result = isTypeReadonly(checker, type);
+          expect(result).toBe(true);
+        });
+      });
+
+      describe('is not readonly', () => {
+        describe('default options', () => {
+          it('fails with a mutable PropertySignature inside a readonly IndexSignature', () => {
+            const { type, checker } = getType(
+              `type Test = { readonly [key: string]: { foo: string[]; }; };`,
+            );
+
+            const result = isTypeReadonly(checker, type);
+            expect(result).toBe(false);
+          });
+        });
+      });
+    });
   });
 });