Rewrite obsolete forgotten intrinsic test (#2647)

that should be part of da020f9 (#2642) commit. See that commit message for reasoning.

core/jvmTest/src/kotlinx/serialization/CachingTest.kt

@@ -60,4 +60,21 @@ class CachingTest {
         val ser3 = serializer(typeOf<Target>())
         assertTrue(SERIALIZERS_CACHE.isStored(Target::class), "Serializer should be stored in cache after typeOf-based lookup")
     }
+
+    @Serializable
+    class Target2
+
+    inline fun <reified T : Any> indirect(): KSerializer<T> = serializer<T>()
+
+    @Test
+    fun testJvmIntrinsicsIndirect() {
+        val ser1 = Target2.serializer()
+        assertFalse(SERIALIZERS_CACHE.isStored(Target2::class), "Cache shouldn't have values before call to serializer<T>()")
+        val ser2 = indirect<Target2>()
+        assertFalse(
+            SERIALIZERS_CACHE.isStored(Target2::class),
+            "Serializer for Target2::class is stored in the cache, which means that runtime lookup was performed and call to serializer<Target2> was not intrinsified." +
+                "Check that compiler plugin intrinsics are enabled and working correctly."
+        )
+    }
 }

formats/json-tests/jvmTest/src/kotlinx/serialization/features/SerializerByTypeTest.kt

@@ -275,18 +275,4 @@ class SerializerByTypeTest {
             serializer(typeTokenOf<Array<NonSerializable>>())
         }
     }
-
-    @OptIn(ExperimentalTime::class)
-    @Test
-    fun testSerializersAreIntrinsified() {
-        val direct = measureTime {
-            Json.encodeToString(IntData.serializer(), IntData(10))
-        }
-        val directMs = direct.inWholeMicroseconds
-        val indirect = measureTime {
-            Json.encodeToString(IntData(10))
-        }
-        val indirectMs = indirect.inWholeMicroseconds
-        if (indirectMs > directMs + (directMs / 4)) error("Direct ($directMs) and indirect ($indirectMs) times are too far apart")
-    }
 }