refactor(utils): 加强 getPriority 方法的优先值判断.

加强优先级判断, 有利于后续使用时防止出现意外情况的问题.
顺便补充一手单元测试.

scalabot-app/src/main/kotlin/util/Utils.kt

@@ -56,9 +56,14 @@ internal fun File.deepListFiles(
  * @return 获取 Finder 的优先级.
  * @throws NoSuchFieldException 如果 Finder 没有添加 [FinderRules] 注解时抛出该异常.
  */
-internal fun ExtensionPackageFinder.getPriority() =
+internal fun ExtensionPackageFinder.getPriority(): Int {
-    this::class.java.getDeclaredAnnotation(FinderRules::class.java)?.priority
+    val value = this::class.java.getDeclaredAnnotation(FinderRules::class.java)?.priority
         ?: throw NoSuchFieldException("Finder did not add `FinderRules` annotation")
+    if (value < 0) {
+        throw IllegalArgumentException("Priority cannot be lower than 0. (Class: ${this::class.java})")
+    }
+    return value
+}
 
 /**
  * 为 [AutoCloseable] 对象注册 Jvm Shutdown 钩子.

scalabot-app/src/test/kotlin/util/UtilsKtTest.kt

@@ -1,9 +1,18 @@
 package net.lamgc.scalabot.util
 
+import net.lamgc.scalabot.ExtensionPackageFinder
+import net.lamgc.scalabot.FinderPriority
+import net.lamgc.scalabot.FinderRules
+import net.lamgc.scalabot.FoundExtensionPackage
+import org.eclipse.aether.artifact.Artifact
 import org.eclipse.aether.artifact.DefaultArtifact
-import org.junit.jupiter.api.Assertions.*
+import org.junit.jupiter.api.assertThrows
-import org.junit.jupiter.api.Test
+import java.io.File
 import java.nio.charset.StandardCharsets
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
 
 internal class UtilsKtTest {
 
@@ -22,4 +31,31 @@ internal class UtilsKtTest {
         assertEquals("48656c6c6f20576f726c64", "Hello World".toByteArray(StandardCharsets.UTF_8).toHexString())
     }
 
+    @Test
+    fun `ExtensionPackageFinder - getPriority`() {
+        open class BaseTestFinder : ExtensionPackageFinder {
+            override fun findByArtifact(extensionArtifact: Artifact, extensionsPath: File): Set<FoundExtensionPackage> {
+                throw IllegalStateException("Calling this class is not allowed.")
+            }
+        }
+
+        @FinderRules(FinderPriority.ALTERNATE)
+        class StandardTestFinder : BaseTestFinder()
+        assertEquals(
+            FinderPriority.ALTERNATE, StandardTestFinder().getPriority(),
+            "获取到的优先值与预期不符"
+        )
+
+        @FinderRules(-1)
+        class OutOfRangePriorityFinder : BaseTestFinder()
+        assertThrows<IllegalArgumentException>("getPriority 方法没有对超出范围的优先值抛出异常.") {
+            OutOfRangePriorityFinder().getPriority()
+        }
+
+        class NoAnnotationFinder : BaseTestFinder()
+        assertThrows<NoSuchFieldException> {
+            NoAnnotationFinder().getPriority()
+        }
+
+    }
 }