Add some tests for CPointer.toKStringFromUtf8

kotlin-native/backend.native/tests/build.gradle

@@ -3805,6 +3805,10 @@ createInterop("cunsupported") {
     it.defFile 'interop/basics/cunsupported.def'
 }
 
+createInterop("ctoKString") {
+    it.defFile 'interop/basics/ctoKString.def'
+}
+
 createInterop("ctypes") {
     it.defFile 'interop/basics/ctypes.def'
 }
@@ -4119,6 +4123,12 @@ interopTest("interop_unsupported") {
     interop = 'cunsupported'
 }
 
+interopTest("interop_toKString") {
+    disabled = (project.testTarget == 'wasm32') // No interop for wasm yet.
+    source = "interop/basics/toKString.kt"
+    interop = 'ctoKString'
+}
+
 interopTest("interop_types") {
     disabled = (project.testTarget == 'wasm32') // No interop for wasm yet.
     source = "interop/basics/types.kt"

kotlin-native/backend.native/tests/interop/basics/ctoKString.def

@@ -0,0 +1,6 @@
+---
+const char* empty() { return ""; }
+const char* foo() { return "foo"; }
+const char* kuku() { return "куку"; }
+const char* invalid_utf8() { return "\x85\xAF"; }
+const char* zero_in_the_middle() { return "before zero\0after zero"; }

kotlin-native/backend.native/tests/interop/basics/toKString.kt

@@ -0,0 +1,12 @@
+import ctoKString.*
+import kotlinx.cinterop.*
+import kotlin.native.*
+import kotlin.test.*
+
+fun main() {
+    assertEquals("", empty()!!.toKStringFromUtf8())
+    assertEquals("foo", foo()!!.toKStringFromUtf8())
+    assertEquals("куку", kuku()!!.toKStringFromUtf8())
+    assertEquals("\uFFFD\uFFFD", invalid_utf8()!!.toKStringFromUtf8())
+    assertEquals("before zero", zero_in_the_middle()!!.toKStringFromUtf8())
+}