Unit Testing a Retrieve TableOperation for Azure Table Storage

Question

I have some code that I'd like to unit test.
I am retrieving some data from an Azure Storage Table database as part of my method that I'd like to test, so I need to mock out the return from the database.

Code to test:

public class GetCustomer : IGetCustomer
{
   //constructor
   public GetCustomer(IClientTableFactory clientTableFactory)
   {
      _partitionKey = "test";
      _customersTable = clientTableFactory.GetStorageTable("customers");
   }

   //method to test
   public async Task<string> GetCustomerNameAsync(string email)
   {
      //match on full email
      var match = await SearchAsync(email.ToLower());
      if (match == null)
      {
         //just match on email domain
         var domain = email.ToLower().Substring(email.IndexOf("@"));
         match = await SearchAsync(domain);
      }
      return match;
   }

   //internal method that queries Azure Table Storage
   private async Task<string> SearchAsync(string searchString)
   {
      var query = TableOperation.Retrieve<Customer>(_partitionKey, rowkey: searchString);
      var result = await _customersTable.ExecuteAsync(query);
      var match = result.Result as Customer;
      return match?.Name;
   }
}

Unit Test so far:

//Arrange
var email = "Testy.McTest@Test.com.au";
var tableFactory = new Mock<IClientTableFactory>();
var customersTable = new Mock<CloudTable>(new Uri("http://unittests.localhost.com/FakeTable"));
customersTable.Setup(x => x.ExecuteAsync(It.IsAny<TableOperation>()))
   .ReturnsAsync(new TableResult{ HttpStatusCode = 200, Result = new Customer{ Name = "jiminy crickets" }});
tableFactory.Setup(x => x.GetStorageTable("customers")).Returns(customersTable.Object);
var getCustomers = new GetCustomer(tableFactory.Object);
// Act
var result = await getCustomers.GetCustomerNameAsync(email);
// Assert
Assert.AreEqual("jiminy crickets", result);

Of course, the test passes every time. The missing piece of the puzzle that I would like to mock out is this line:

customersTable
    .Setup(x => x.ExecuteAsync(It.IsAny<TableOperation>()))
    .ReturnsAsync...

I should be able to replace It.IsAny<TableOperation>() with my search query eg It.Is<TableOperation>(y => y.RowKey == "testy.mctest@test.com.au" but unfortunately RowKey is inaccessible.

I've also tried

customersTable
    .Setup(x => x.ExecuteAsync(TableOperation.Retrieve<Customer>(_partitionKey, rowkey: searchString))

but it never passes this code at runtime - maybe because of the ETag property?

Any ideas? I've seen plenty of answers about mocking Table Storage, but none about mocking Query results.

Answer 1

If you don't mind using reflection you can find the values in the internal members "RetrievePartitionKey" and "RetrieveRowKey".

I wrote a simple method:

  private T GetInternalMember<T>(object obj, string propertyName)
    {
        Type objType = obj.GetType();
        PropertyInfo propInfo = objType.GetProperty(propertyName,
                BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);

        return (T)propInfo.GetValue(obj, null);
    }

And I'm using it like:

cloudTable.Verify(x => x.ExecuteAsync(It.Is<TableOperation>(op => GetInternalMember<string>(op, "RetrievePartitionKey") == "TestPartitionKey"
                                                                           && GetInternalMember<string>(op, "RetrieveRowKey") == "TestRowKey")));

It's not really ideal, but it works for unit tests.