Csharp 如何使用moq和xUnit对删除操作进行单元测试

我正在try 对我的Web API项目中的API的CRUD操作进行单元测试.我费了好大劲才弄明白如何删除.下面是我的服务；

public async Task DeleteCompany(int id)
{
    var query = "DELETE FROM Companies WHERE Id = @Id";
    using(var connection = _context.CreateConnection())
    {
        await connection.ExecuteAsync(query, new {id});
    }
}

这是控制器

[HttpDelete("{id}")]
public async Task<IActionResult> DeleteCompany(int id)
{
    var company = await _companyRepository.GetCompanyById(id);
    if (company == null)
    {
        return NotFound();
    }
    await _companyRepository.DeleteCompany(id);
    return NoContent();
}

下面是单元测试的代码

[Theory]
[InlineData(1)]
public async Task CompanyController_DeleteCompany_ShouldReturnStatusCode204(int id)
{
    var mockCompany = new Mock<ICompanyRepository>();
    mockCompany.Setup(service => service.DeleteCompany(id))
           .Returns(Task.CompletedTask)
           .Verifiable();

    var sut = new CompanyController(mockCompany.Object);

    var result = (OkObjectResult) await sut.DeleteCompany(id);

    result.StatusCode.Should().Be(204);
}

结果是，在调试之后，它返回了我的模型(在本例中为Company)的空值.这就是为什么测试没有通过，并且控制器中出现了NotFound个错误.