Add tests

Author: ahejlsberg

tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts

@@ -141,3 +141,19 @@ function test1<T extends Record<string, any>, K extends keyof T>(t: T, k: K) {
     t[k] = "hello";  // Error
     t[k] = [10, 20];  // Error
 }
+
+// Repro from #28839
+
+function f30<T, K extends keyof T>() {
+    let x: Partial<Record<keyof T, string>>[K] = "hello";
+}
+
+// We simplify indexed accesses applied to mapped types up to five levels deep
+
+function f31<T, K extends keyof T>() {
+    let x: Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>[K] = "hello";
+}
+
+function f32<T, K extends keyof T>() {
+    let x: Partial<Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>>[K] = "hello";
+}