如何使用假冒轻松设置测试中的自动增量ID

Question

场景

我在PreviewService.AddPreview中有方法。我想测试它是否添加新的预览。我使用C＃和EntityFremework。如何通过自动增量编程测试以创建预览ID？我知道我应该拥有存储库或DAO，但我无权对其进行重构：（。

代码

private DbSet<WebsitePreview> _previewDbSet;
private List<WebsitePreview> _previews;
private IQueryable<WebsitePreview> _previewsAsQueryable => this._previews.AsQueryable();  

在设置中

_previews = new List<WebsitePreview>();
_previewDbSet = A.Fake<DbSet<WebsitePreview>>(cat =>
    cat.Implements<IQueryable<WebsitePreview>>());
A.CallTo(() => ((IQueryable<WebsitePreview>)_previewDbSet).Provider)
    .Returns(_previewsAsQueryable.Provider);
A.CallTo(() => ((IQueryable<WebsitePreview>)_previewDbSet).GetEnumerator())
    .Returns(_previewsAsQueryable.GetEnumerator());
A.CallTo(() => ((IQueryable<WebsitePreview>)_previewDbSet).Expression)
   .Returns(_previewsAsQueryable.Expression);
A.CallTo(() => ((IQueryable<WebsitePreview>)_previewDbSet).ElementType)
   .Returns(this._previewsAsQueryable.ElementType);
A.CallTo(() => _dbContext.Set<WebsitePreview>()).Returns(_previewDbSet);

测试

//arrange
string newPreviewName = "new";
WebsitePreview existingPreview = GetExistingPreview();     //it has id=1
this._previews.Add(existingPreview);
PreviewItemDto expectedPreviewItemDto = new PreviewItemDto
{
    Id = 2,
    Name = "new",
    Selected = false
};

//act
var result = this._sut.AddNewPreview(newPreviewName);
//assert
//(2, 0)
Assert.AreEqual(expectedPreviewItemDto.Id, result.Id); //result.Id equals 0, expected 2