added TelegramDate tests and fix in chat identifier functionality

src/main/kotlin/com/github/insanusmokrassar/TelegramBotAPI/types/ChatIdentifier.kt

@@ -51,7 +51,7 @@ internal object ChatIdentifierSerializer : KSerializer<ChatIdentifier> {
 
     override fun serialize(encoder: Encoder, obj: ChatIdentifier) {
         when (obj) {
-            is ChatId -> encoder.encodeString(obj.chatId.toString())
+            is ChatId -> encoder.encodeLong(obj.chatId)
             is Username -> encoder.encodeString(obj.username)
         }
     }

src/main/kotlin/com/github/insanusmokrassar/TelegramBotAPI/types/TelegramDate.kt

@@ -5,7 +5,10 @@ import org.joda.time.DateTime
 import java.util.concurrent.TimeUnit
 
 @Serializable(TelegramDateSerializer::class)
-class TelegramDate(
+data class TelegramDate(
+    /**
+     * Contains UNIX time (seconds)
+     */
     private val date: Long
 ) {
     constructor(dateTime: DateTime) : this(

src/test/kotlin/com/github/insanusmokrassar/TelegramBotAPI/types/ChatIdentifierTests.kt

@@ -55,7 +55,7 @@ class ChatIdentifierTests {
 
         Example(chatIdentifierChatId.toChatId()).let { withChatId ->
             val stringified = Json.plain.stringify(Example.serializer(), withChatId)
-            assertEquals(stringified, "{\"identifier\":\"$chatIdentifierChatId\"}")
+            assertEquals(stringified, "{\"identifier\":$chatIdentifierChatId}")
             val deserialized = Json.plain.parse(Example.serializer(), stringified)
             assertEquals(withChatId, deserialized)
         }

src/test/kotlin/com/github/insanusmokrassar/TelegramBotAPI/types/TelegramDateTests.kt

@@ -0,0 +1,33 @@
+package com.github.insanusmokrassar.TelegramBotAPI.types
+
+import kotlinx.serialization.ImplicitReflectionSerializer
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.Json
+import org.joda.time.DateTime
+import java.util.concurrent.TimeUnit
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+private val dateTimeMillis = System.currentTimeMillis()
+private val dateTimeUnix = TimeUnit.MILLISECONDS.toSeconds(dateTimeMillis)
+private val dateTime = DateTime(TimeUnit.SECONDS.toMillis(dateTimeUnix))
+
+@ImplicitReflectionSerializer
+class TelegramDateTests {
+    @Serializable
+    data class Example(
+        val dateTime: TelegramDate
+    )
+    @Test
+    fun `Serializtion of TelegramDate is working correctly`() {
+        val example = Example(TelegramDate(dateTimeUnix))
+
+        val stringified = Json.plain.stringify(Example.serializer(), example)
+        assertEquals("{\"dateTime\":$dateTimeUnix}", stringified)
+
+        val deserialized = Json.plain.parse(Example.serializer(), stringified)
+        assertEquals(example, deserialized)
+
+        assertEquals(dateTime, deserialized.dateTime.asDate)
+    }
+}