A very contrived example of using a test double for CloudTable using NSubstitute in a unit test

ContrivedUnitTestWithCloudTable.cs

// This is not runnable as is, but shows the basic principle. Note that the cloud table test double is being used as a stub, 
// not a spy or a mock, although it could fulfill either of those roles with additional setup if required.
[Fact]
public async Task ExampleUnitTestWithCloudTableTestDouble()
{
    var testResult = new TableResult
    {
        Result = new MyEntity()
        {
            ETag = "*",
            PartitionKey = "PartitionKey",
            RowKey = "RowKey",
            MyProperty = "SomeValue"
        },
        HttpStatusCode = 200
    };

    var subCloudTable = Substitute.For<CloudTable>(new Uri("tempuir.org"));

    subCloudTable.ExecuteAsync(Arg.Any<TableOperation>()).Returns(testResult);
    
    var actual = await sut.DoSomething(subCloudTable);

    actual.Should().Be(expected);
}