add exceptions

src/main/kotlin/com/infendro/migration/Migration.kt

@@ -1,5 +1,6 @@
 package com.infendro.migration
 
+import com.infendro.migration.exception.DuplicateMigrationException
 import com.infendro.migration.model.MigrationRepository
 import com.infendro.migration.model.MigrationTable
 import org.jetbrains.exposed.sql.SchemaUtils
@@ -53,6 +54,10 @@ class Config {
         name: String,
         migrate: Transaction.() -> Unit,
     ) {
+        if (migrations.any { it.name == name }) {
+            throw DuplicateMigrationException(name)
+        }
+
         migrations += Migration(name, migrate)
     }
 

src/main/kotlin/com/infendro/migration/exception/DuplicateMigrationException.kt

@@ -0,0 +1,5 @@
+package com.infendro.migration.exception
+
+class DuplicateMigrationException(
+    val name: String,
+) : Exception()