sealed class test using deduction instead of field

Add a test that verifies we can deserialize sealed classes using `JsonTypeInfo.Id.DEDUCTION` instead of explicit field names.

Author: Dariusz Kuc

src/test/kotlin/com/fasterxml/jackson/module/kotlin/test/SealedClassTest.kt

@@ -1,9 +1,13 @@
 package com.fasterxml.jackson.module.kotlin.test
 
+import com.fasterxml.jackson.annotation.JsonCreator
+import com.fasterxml.jackson.annotation.JsonSubTypes
 import com.fasterxml.jackson.annotation.JsonTypeInfo
+import com.fasterxml.jackson.annotation.JsonValue
 import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
 import com.fasterxml.jackson.module.kotlin.test.SealedClassTest.SuperClass.B
 import org.junit.Test
+import kotlin.test.assertEquals
 import kotlin.test.assertTrue
 
 class SealedClassTest {
@@ -23,9 +27,33 @@ class SealedClassTest {
         assertTrue { result is B }
     }
 
+    /**
+     * Tests that we can use JsonTypeInfo.Id.DEDUCTION to deduct sealed types without the need for explicit fields.
+     */
+    @Test
+    fun sealedClassWithoutTypeDiscriminator() {
+        val serializedSingle = """{"request":"single"}"""
+        val single = mapper.readValue(serializedSingle, SealedRequest::class.java)
+        assertTrue(single is SealedRequest.SingleRequest)
+        assertEquals("single", single.request)
+
+        val serializedBatch = """[{"request":"first"},{"request":"second"}]"""
+        val batch = mapper.readValue(serializedBatch, SealedRequest::class.java)
+        assertTrue(batch is SealedRequest.BatchRequest)
+        assertEquals(2, batch.requests.size)
+        assertEquals("first", batch.requests[0].request)
+        assertEquals("second", batch.requests[1].request)
+    }
+
     @JsonTypeInfo(use = JsonTypeInfo.Id.NAME)
     sealed class SuperClass {
         class A : SuperClass()
         class B : SuperClass()
     }
+
+    @JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION)
+    sealed class SealedRequest {
+        data class SingleRequest(val request: String) : SealedRequest()
+        data class BatchRequest @JsonCreator constructor(@get:JsonValue val requests: List<SingleRequest>): SealedRequest()
+    }
 }