Add test for NSMutableString -> kotlin.String -> NSString conversion

backend.native/tests/framework/values/expectedLazy.h

@@ -1030,6 +1030,14 @@ __attribute__((swift_name("GH3525")))
 + (instancetype)gH3525 __attribute__((swift_name("init()")));
 @end;
 
+__attribute__((objc_subclassing_restricted))
+__attribute__((swift_name("TestStringConversion")))
+@interface ValuesTestStringConversion : ValuesBase
+- (instancetype)init __attribute__((swift_name("init()"))) __attribute__((objc_designated_initializer));
++ (instancetype)new __attribute__((availability(swift, unavailable, message="use object initializers instead")));
+@property id str __attribute__((swift_name("str")));
+@end;
+
 @interface ValuesEnumeration (ValuesKt)
 - (ValuesEnumeration *)getAnswer __attribute__((swift_name("getAnswer()")));
 @end;

backend.native/tests/framework/values/values.kt

@@ -826,4 +826,8 @@ object GH3525 : GH3525Base() {
     init {
         gh3525InitCount++
     }
+}
+
+class TestStringConversion {
+    lateinit var str: Any
 }

backend.native/tests/framework/values/values.swift

@@ -1077,6 +1077,19 @@ func testGH3525() throws {
     try assertTrue(gh3525_1 === gh3525_2)
 }
 
+func testStringConversion() throws {
+    let test = TestStringConversion()
+
+    let buffer = NSMutableString()
+    buffer.append("a")
+    test.str = buffer
+    buffer.append("b")
+
+    try assertEquals(actual: buffer, expected: "ab")
+    // Ensure test.str isn't affected by buffer mutation:
+    try assertEquals(actual: test.str as! NSString, expected: "a")
+}
+
 // -------- Execution of the test --------
 
 class ValuesTests : TestProvider {
@@ -1132,6 +1145,7 @@ class ValuesTests : TestProvider {
             TestCase(name: "TestGH3503_2", method: withAutorelease(testGH3503_2)),
             TestCase(name: "TestGH3503_3", method: withAutorelease(testGH3503_3)),
             TestCase(name: "TestGH3525", method: withAutorelease(testGH3525)),
+            TestCase(name: "TestStringConversion", method: withAutorelease(testStringConversion)),
 
             // Stress test, must remain the last one:
             TestCase(name: "TestGH2931", method: withAutorelease(testGH2931)),