diff --git a/Heim/Presentation/PresentationTests/ViewModel/DiaryDetailViewModelTests.swift b/Heim/Presentation/PresentationTests/ViewModel/DiaryDetailViewModelTests.swift
new file mode 100644
index 0000000..3806e83
--- /dev/null
+++ b/Heim/Presentation/PresentationTests/ViewModel/DiaryDetailViewModelTests.swift
@@ -0,0 +1,134 @@
+//
+//  DiaryDetailViewModelTests.swift
+//  PresentationTests
+//
+//  Created by 박성근 on 12/6/24.
+//
+
+import XCTest
+@testable import Presentation
+import Domain
+
+final class DiaryDetailViewModelTests: XCTestCase {
+  private var sut: DiaryDetailViewModel!
+  private var mockDiaryUseCase: MockDiaryUseCase!
+  private var mockUserUseCase: MockUserUseCase!
+  private var testDiary: Diary!
+  
+  override func setUp() {
+    super.setUp()
+    mockDiaryUseCase = MockDiaryUseCase()
+    mockUserUseCase = MockUserUseCase()
+    
+    let testDate = CalendarDate(
+      year: 2024,
+      month: 12,
+      day: 6,
+      hour: 12,
+      minute: 0,
+      second: 0
+    )
+    
+    testDiary = Diary(
+      calendarDate: testDate,
+      emotion: .happiness,
+      emotionReport: EmotionReport(text: "Test Report"),
+      voice: Voice(audioBuffer: Data()),
+      summary: Summary(text: "Test Summary")
+    )
+    
+    sut = DiaryDetailViewModel(
+      diaryUseCase: mockDiaryUseCase,
+      userUseCase: mockUserUseCase,
+      diary: testDiary
+    )
+  }
+  
+  override func tearDown() {
+    sut = nil
+    mockDiaryUseCase = nil
+    mockUserUseCase = nil
+    testDiary = nil
+    super.tearDown()
+  }
+  
+  // MARK: - Initial State Tests
+  func test_initialState() {
+    XCTAssertEqual(sut.state.calendarDate, "")
+    XCTAssertEqual(sut.state.emotion, "")
+    XCTAssertEqual(sut.state.description, "")
+    XCTAssertEqual(sut.state.content, "")
+    XCTAssertFalse(sut.state.isDeleted)
+    XCTAssertFalse(sut.state.isErrorPresent)
+  }
+  
+  // MARK: - Fetch Diary Tests
+  func test_givenSuccessfulResponse_whenFetchDiary_thenUpdatesState() async throws {
+    // When
+    sut.action(.fetchDiary)
+    
+    // Then
+    try await Task.sleep(nanoseconds: 100_000_000)
+    
+    XCTAssertEqual(sut.state.calendarDate, "2024년 12월 6일")
+    XCTAssertEqual(sut.state.emotion, "happiness")
+    XCTAssertEqual(sut.state.content, "Test Summary")
+    XCTAssertEqual(mockUserUseCase.fetchUserNameCallCount, 1)
+  }
+  
+  func test_givenError_whenFetchDiary_thenUsesDefaultUserName() async throws {
+    // Given
+    mockUserUseCase.shouldThrowError = true
+    
+    // When
+    sut.action(.fetchDiary)
+    
+    // Then
+    try await Task.sleep(nanoseconds: 100_000_000)
+    
+    XCTAssertEqual(sut.userName, "User")
+    XCTAssertEqual(sut.state.calendarDate, "2024년 12월 6일")
+    XCTAssertEqual(sut.state.emotion, "happiness")
+    XCTAssertEqual(sut.state.content, "Test Summary")
+  }
+  
+  // MARK: - Delete Diary Tests
+  func test_givenSuccessfulResponse_whenDeleteDiary_thenUpdatesState() async throws {
+    // When
+    sut.action(.deleteDiary)
+    
+    // Then
+    try await Task.sleep(nanoseconds: 100_000_000)
+    
+    XCTAssertTrue(sut.state.isDeleted)
+    XCTAssertFalse(sut.state.isErrorPresent)
+    XCTAssertEqual(mockDiaryUseCase.deleteDiaryCallCount, 1)
+  }
+  
+  func test_givenError_whenDeleteDiary_thenSetsErrorState() async throws {
+    // Given
+    mockDiaryUseCase.shouldThrowError = true
+    
+    // When
+    sut.action(.deleteDiary)
+    
+    // Then
+    try await Task.sleep(nanoseconds: 100_000_000)
+    
+    XCTAssertFalse(sut.state.isDeleted)
+    XCTAssertTrue(sut.state.isErrorPresent)
+    XCTAssertEqual(mockDiaryUseCase.deleteDiaryCallCount, 1)
+  }
+  
+  // MARK: - Clear Error Tests
+  func test_whenClearError_thenResetsErrorState() {
+    // Given
+    sut.state.isErrorPresent = true
+    
+    // When
+    sut.action(.clearError)
+    
+    // Then
+    XCTAssertFalse(sut.state.isErrorPresent)
+  }
+}