【C#/Blazor】実務Webアプリ開発編(24)Domain層のテストを書く ～値オブジェクト・エンティティ・集約・ドメインサービスを外部依存なしで検証する～

Arrange：テスト対象と入力値を用意する
  ↓
Act：コンストラクタやメソッドを実行する
  ↓
Assert：期待した結果・例外・状態になっているか確認する

[Fact]
public void CreateEmail_WithWhitespace_Then_TrimsValue()
{
    // Arrange
    const string input = "  taro.yamada@example.com  ";
    const string expected = "taro.yamada@example.com";

    // Act
    var email = new Email(input);

    // Assert
    Assert.Equal(expected, email.Value);
    Assert.Equal(expected, email.ToString());
}

[Theory]
[InlineData(null)]
[InlineData("abc")]
public void CreateEmail_WithInvalidValue_Then_ThrowsArgumentException(string? input)
{
    // Act & Assert
    Assert.Throws<ArgumentException>(() => new Email(input));
}

[Fact]
public void CreateUser_Then_PropertiesAreInitialized()
{
    // Arrange
    var createdAt = new DateTimeOffset(2026, 1, 15, 10, 0, 0, TimeSpan.Zero);
    const string externalId = "mentor-001";
    const string displayName = "山田太郎";
    const string email = "taro.yamada@example.com";

    // Act
    var user = new User(externalId, displayName, createdAt, email, Role.Mentor);

    // Assert
    Assert.NotEqual(Guid.Empty, user.Id);
    Assert.Equal(externalId, user.ExternalId);
    Assert.Equal(displayName, user.DisplayName);
    Assert.Equal(email, user.Email.Value);
    Assert.Equal(Role.Mentor, user.Role);
    Assert.Equal(createdAt, user.CreatedAt);
}

[Fact]
public void UpdateDisplayName_WithBlankName_Then_ThrowsArgumentException()
{
    // Arrange
    const string externalId = "mentee-001";
    const string currentDisplayName = "佐藤花子";
    const string email = "hanako.sato@example.com";

    var user = new User(
        externalId: externalId,
        displayName: currentDisplayName,
        createdAt: new DateTimeOffset(2026, 1, 15, 10, 0, 0, TimeSpan.Zero),
        email: email,
        role: Role.Mentee);

    // Act & Assert
    Assert.Throws<ArgumentException>(() => user.UpdateDisplayName("   "));

    // Assert
    Assert.Equal(currentDisplayName, user.DisplayName);
}

[Fact]
public void CreateTopic_Then_InitialStateIsOpen()
{
    // Arrange
    var mentorshipId = Guid.NewGuid();
    var createdAt = new DateTimeOffset(2026, 1, 15, 10, 0, 0, TimeSpan.Zero);
    const string title = "相談したいこと";

    // Act
    var topic = new Topic(mentorshipId, title, createdAt);

    // Assert
    Assert.NotEqual(Guid.Empty, topic.Id);
    Assert.Equal(mentorshipId, topic.MentorshipId);
    Assert.Equal(title, topic.Title);
    Assert.Equal(TopicStatus.Open, topic.Status);
    Assert.Equal(createdAt, topic.CreatedAt);
    Assert.Empty(topic.Messages);
}

[Fact]
public void CloseTopic_Then_CannotPostMessage()
{
    // Arrange
    var topic = new Topic(Guid.NewGuid(), "クローズ確認", new DateTimeOffset(2026, 1, 15, 10, 0, 0, TimeSpan.Zero));
    var senderUserId = Guid.NewGuid();
    const string messageContent = "クローズ後の投稿";

    topic.Close();

    // Act & Assert
    Assert.Throws<InvalidOperationException>(() =>
        topic.PostMessage(senderUserId, messageContent, new DateTimeOffset(2026, 1, 15, 11, 0, 0, TimeSpan.Zero)));

    // Assert
    Assert.Equal(TopicStatus.Closed, topic.Status);
    Assert.Empty(topic.Messages);
}

[Fact]
public void ValidateMentorshipCreation_WithoutActiveMentorship_Then_DoesNotThrow()
{
    // Arrange
    var service = new MentorshipDuplicationCheckService();
    var mentor = CreateUser("mentor-001", "テストメンター", "mentor@example.com", Role.Mentor);
    var mentee = CreateUser("mentee-001", "テストメンティー", "mentee@example.com", Role.Mentee);

    // Act
    var exception = Record.Exception(() =>
        service.ValidateMentorshipCreation(mentor, mentee, hasActiveMentorshipForPair: false));

    // Assert
    Assert.Null(exception);
}

[Fact]
public void ValidateMentorshipCreation_WithActiveMentorship_Then_ThrowsInvalidOperationException()
{
    // Arrange
    var service = new MentorshipDuplicationCheckService();
    var mentor = CreateUser("mentor-001", "テストメンター", "mentor@example.com", Role.Mentor);
    var mentee = CreateUser("mentee-001", "テストメンティー", "mentee@example.com", Role.Mentee);

    // Act & Assert
    Assert.Throws<InvalidOperationException>(() =>
        service.ValidateMentorshipCreation(mentor, mentee, hasActiveMentorshipForPair: true));
}