diff --git a/src/test/kotlin/roomescape/supports/TestUtil.kt b/src/test/kotlin/roomescape/supports/TestUtil.kt
index 10c4d735..8b5780e5 100644
--- a/src/test/kotlin/roomescape/supports/TestUtil.kt
+++ b/src/test/kotlin/roomescape/supports/TestUtil.kt
@@ -12,14 +12,15 @@ inline fun <T> initialize(name: String, block: () -> T): T {
 
 fun randomPhoneNumber(): String {
     val prefix = "010"
-    val middle = (1000..9999).random()
-    val last = (1000..9999).random()
+    val middle = (1..4).map {  (0..9).random() }.joinToString("")
+    val last = (1..4).map {  (0..9).random() }.joinToString("")
+
     return "$prefix$middle$last"
 }
 
-fun randomString(): String {
+fun randomString(length: Int = 10): String {
     val chars = ('a'..'z') + ('0'..'9')
-    return (1..10)
+    return (1..length)
         .map { chars.random() }
         .joinToString("")
 }