fix: classloaderの呼び出しを変更

src/main/kotlin/dev/usbharu/hideout/routing/UserRouting.kt

@@ -67,7 +67,7 @@ fun Application.user(userService: UserService, activityPubUserService: ActivityP
                     }
                 }
                 get("/{name}/icon.png"){
-                    call.respondBytes(Application::class.java.classLoader.getResourceAsStream("/icon.png").readAllBytes(),ContentType.Image.PNG)
+                    call.respondBytes(javaClass.classLoader.getResourceAsStream("icon.png").readAllBytes(),ContentType.Image.PNG)
                 }
             }
 

src/test/kotlin/dev/usbharu/hideout/routing/UserRoutingKtTest.kt

@@ -0,0 +1,12 @@
+package dev.usbharu.hideout.routing
+
+import org.junit.jupiter.api.Test
+
+class UserRoutingKtTest {
+    @Test
+    fun userIconTest() {
+        println(String.Companion::class.java.classLoader)
+        println(String::class.java.classLoader)
+        println(String.javaClass.classLoader.getResourceAsStream("icon.png")?.readAllBytes())
+    }
+}