diff --git a/yls/src/main/kotlin/com/yourssu/logging/system/HashUtil.kt b/yls/src/main/kotlin/com/yourssu/logging/system/HashUtil.kt
new file mode 100644
index 0000000..9eff744
--- /dev/null
+++ b/yls/src/main/kotlin/com/yourssu/logging/system/HashUtil.kt
@@ -0,0 +1,30 @@
+package com.yourssu.logging.system
+
+import java.lang.StringBuilder
+import java.security.MessageDigest
+
+object HashUtil {
+    // 캐싱
+    private var _id: String? = null
+    private var _hashedId: String? = null
+
+    fun hashId(id: String): String {
+        if (_id == id && _hashedId != null) {
+            return _hashedId!!
+        }
+
+        _hashedId = hashString(id)
+        _id = id
+        return _hashedId!!
+    }
+
+    internal fun hashString(origin: String, algorithm: String = "SHA-256"): String {
+        return MessageDigest.getInstance(algorithm)
+            .digest(origin.toByteArray())
+            .let { bytes ->
+                bytes.fold(StringBuilder(bytes.size * 2)) { str, it ->
+                    str.append("%02x".format(it))
+                }
+            }.toString()
+    }
+}
diff --git a/yls/src/main/kotlin/com/yourssu/logging/system/YLS.kt b/yls/src/main/kotlin/com/yourssu/logging/system/YLS.kt
index bb2ec75..7ed8c61 100644
--- a/yls/src/main/kotlin/com/yourssu/logging/system/YLS.kt
+++ b/yls/src/main/kotlin/com/yourssu/logging/system/YLS.kt
@@ -2,19 +2,14 @@ package com.yourssu.logging.system
 
 import android.annotation.SuppressLint
 import android.content.Context
-import android.os.Build.VERSION
-import android.os.Build.VERSION_CODES
 import android.util.Log
 import androidx.work.OneTimeWorkRequestBuilder
 import androidx.work.WorkManager
 import androidx.work.workDataOf
 import com.google.gson.Gson
+import com.yourssu.logging.system.HashUtil.hashId
 import com.yourssu.logging.system.worker.RemoteLoggingWorker
-import java.lang.StringBuilder
-import java.security.MessageDigest
 import java.text.SimpleDateFormat
-import java.time.LocalDateTime
-import java.time.ZoneOffset
 import java.util.Date
 
 class YLS private constructor() {
@@ -33,6 +28,7 @@ class YLS private constructor() {
         }
 
         open fun flush() {
+            if (queue.isEmpty()) return
             log(queue)
             queue.clear()
         }
@@ -70,16 +66,18 @@ class YLS private constructor() {
 
         fun init(
             platform: String,
-            user: String?,
+            user: String,
             logger: Logger,
         ) {
             this.defaultEvent = mapOf("platform" to platform)
-            this.userID = user ?: generateRandomId(10)
+            this.userID = user
             this.logger = logger
         }
 
         fun log(vararg events: Pair<String, Any>) {
-            if (!::logger.isInitialized) throw AssertionError("Not Initialized!")
+            if (!::logger.isInitialized) {
+                throw AssertionError("Not initialized! : YLS.init()을 먼저 호출해 주세요.")
+            }
 
             val eventData = YLSEventData(
                 hashedID = hashId(userID),
@@ -90,40 +88,19 @@ class YLS private constructor() {
         }
 
         fun flush() {
+            if (!::logger.isInitialized) {
+                throw AssertionError("Not initialized! : YLS.init()을 먼저 호출해 주세요.")
+            }
             logger.flush()
         }
 
-        internal fun generateRandomId(length: Int): String {
+        fun generateRandomId(length: Int): String {
             val charset = '!'..'~' // ASCII 33 ~ 126
             return (1..length).map { charset.random() }.joinToString("")
         }
 
-        // hashId() 메서드에서만 사용되는 변수
-        private var _id: String? = null
-        private var _hashedId: String? = null
-
-        internal fun hashId(id: String): String {
-            if (_id == id && _hashedId != null) {
-                return _hashedId!!
-            }
-            return id.hashString().also {
-                _id = id
-                _hashedId = it
-            }
-        }
-
         @SuppressLint("SimpleDateFormat")
-        internal fun getTimestampISO8601(): String =
+        fun getTimestampISO8601(): String =
             SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'").format(Date())
     }
 }
-
-internal fun String.hashString(algorithm: String = "SHA-256"): String {
-    return MessageDigest.getInstance(algorithm)
-        .digest(this.toByteArray())
-        .let { bytes ->
-            bytes.fold(StringBuilder(bytes.size * 2)) { str, it ->
-                str.append("%02x".format(it))
-            }
-        }.toString()
-}
diff --git a/yls/src/main/kotlin/com/yourssu/logging/system/worker/RemoteLoggingWorker.kt b/yls/src/main/kotlin/com/yourssu/logging/system/worker/RemoteLoggingWorker.kt
index ea81d87..b754972 100644
--- a/yls/src/main/kotlin/com/yourssu/logging/system/worker/RemoteLoggingWorker.kt
+++ b/yls/src/main/kotlin/com/yourssu/logging/system/worker/RemoteLoggingWorker.kt
@@ -4,7 +4,6 @@ import android.content.Context
 import androidx.work.CoroutineWorker
 import androidx.work.WorkerParameters
 import com.google.gson.Gson
-import com.yourssu.logging.system.HttpService
 import com.yourssu.logging.system.YLSEventData
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
diff --git a/yls/src/main/kotlin/com/yourssu/logging/system/Retrofit.kt b/yls/src/main/kotlin/com/yourssu/logging/system/worker/Retrofit.kt
similarity index 72%
rename from yls/src/main/kotlin/com/yourssu/logging/system/Retrofit.kt
rename to yls/src/main/kotlin/com/yourssu/logging/system/worker/Retrofit.kt
index 7463e88..5e20060 100644
--- a/yls/src/main/kotlin/com/yourssu/logging/system/Retrofit.kt
+++ b/yls/src/main/kotlin/com/yourssu/logging/system/worker/Retrofit.kt
@@ -1,5 +1,6 @@
-package com.yourssu.logging.system
+package com.yourssu.logging.system.worker
 
+import com.yourssu.logging.system.YLSEventData
 import retrofit2.Response
 import retrofit2.http.Body
 import retrofit2.http.PUT
diff --git a/yls/src/test/kotlin/com/yourssu/logging/system/LoggingTest.kt b/yls/src/test/kotlin/com/yourssu/logging/system/LoggingTest.kt
index fefc0bf..6fcc696 100644
--- a/yls/src/test/kotlin/com/yourssu/logging/system/LoggingTest.kt
+++ b/yls/src/test/kotlin/com/yourssu/logging/system/LoggingTest.kt
@@ -1,5 +1,7 @@
 package com.yourssu.logging.system
 
+import com.yourssu.logging.system.HashUtil.hashId
+import com.yourssu.logging.system.HashUtil.hashString
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
 import org.junit.Before
@@ -41,12 +43,15 @@ class LoggingTest {
             "screen" to "LoginScreen",
         )
 
-        testLogger.lastEventData?.let {
-            assertEquals("abc".hashString(), it.hashedID)
-            assertEquals("android", it.event["platform"])
-            assertEquals("ButtonClicked", it.event["event"])
-            assertEquals("LoginScreen", it.event["screen"])
-        } ?: assertTrue(false) // if null, then fail
+        val e = testLogger.lastEventData
+        if (e != null) {
+            assertEquals(hashString("abc"), e.hashedID)
+            assertEquals("android", e.event["platform"])
+            assertEquals("ButtonClicked", e.event["event"])
+            assertEquals("LoginScreen", e.event["screen"])
+        } else {
+            assertTrue(false) // always fail
+        }
     }
 
     @Test
@@ -74,6 +79,6 @@ class LoggingTest {
         // 함수 테스트
         println(YLS.generateRandomId(10))
         println(YLS.getTimestampISO8601())
-        println(YLS.hashId("abc"))
+        println(hashId("abc"))
     }
 }