Add test for unique packet IDs

blokk-packet-codecs/build.gradle.kts

@@ -7,19 +7,35 @@ version = rootProject.version
 
 repositories {
     mavenCentral()
+    jcenter()
 }
 
 val nettyVersion = properties["version.netty"].toString()
+val junitVersion = properties["version.junit"].toString()
+val striktVersion = properties["version.strikt"].toString()
 
 dependencies {
     api(project(":blokk-packets"))
 
     // Netty
     api("io.netty:netty-buffer:${nettyVersion}")
+
+    // Testing
+    testImplementation("io.strikt:strikt-core:${striktVersion}")
+    testImplementation("org.junit.jupiter:junit-jupiter-api:${junitVersion}")
+    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:${junitVersion}")
 }
 
 tasks {
     compileKotlin {
         kotlinOptions.jvmTarget = "1.8"
     }
+
+    compileTestKotlin {
+        kotlinOptions.jvmTarget = "1.8"
+    }
+
+    test {
+        useJUnitPlatform()
+    }
 }

blokk-packet-codecs/src/test/kotlin/space/blokk/net/packets/ProtocolValidationTest.kt

@@ -0,0 +1,33 @@
+package space.blokk.net.packets
+
+import org.junit.jupiter.api.Test
+import space.blokk.net.packets.handshaking.HandshakingProtocol
+import space.blokk.net.packets.login.LoginProtocol
+import space.blokk.net.packets.play.PlayProtocol
+import space.blokk.net.packets.status.StatusProtocol
+
+class ProtocolValidationTest {
+    private fun ensureIDUniqueness(codecs: List<PacketCodec<*>>, type: String, protocol: Protocol) {
+        codecs.groupBy { it.id }.forEach { (id, c) ->
+            if (c.count() > 1) {
+                val packetsString = c.joinToString(", ", limit = 4) { it.dataType.simpleName.toString() }
+                throw AssertionError(
+                    "Multiple $type packets of the ${protocol.name} protocol use the same ID " +
+                            "(0x${id.toString(16)}): $packetsString"
+                )
+            }
+        }
+    }
+
+    @Test
+    fun `all packets have unique IDs in their protocol`() {
+        for (protocol in PROTOCOLS) {
+            ensureIDUniqueness(protocol.codecs.filterIsInstance<IncomingPacketCodec<*>>(), "incoming", protocol)
+            ensureIDUniqueness(protocol.codecs.filterIsInstance<OutgoingPacketCodec<*>>(), "outgoing", protocol)
+        }
+    }
+
+    companion object {
+        val PROTOCOLS = setOf(HandshakingProtocol, LoginProtocol, StatusProtocol, PlayProtocol)
+    }
+}