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Approval CSharp kata

Objectives

  • Discover how and why use an object-object mapper library
  • Practice Approval testing approach and discover how powerful it can be with several Use Cases :
    • Check mappings
    • Check API results in Integration Tests
    • Check non deterministic data
    • Combination approvals

Prerequisites

  • .NET 6
  • Your favorite IDE
  • Access to nuget.org

Libraries

Step-by-step kata

1) Object-object mapper

  • Fix the test Should_Map_Employee_To_EmployeeEntity by using Auto-Mapper
    • What is surprising you ?
    • How could it be helpful in your current projects ?
  • Add a new "feature" that brings mapping from PersonAccount to IndividualParty
    • Discuss how easy it is to add new mappings

2) Approval Testing

Also called : Characterization Tests OR Snapshot Tests or Golden Master

A picture’s worth a 1000 tests.

  • Unit testing assertions can be difficult to use and long to write
  • Approval tests simplify this by taking a snapshot of the results / confirming that they have not changed at each run

This technique can be used on :

  • On any new code
  • On legacy code

Check your mapping

  • Add a new test to check this mapping PersonAccount -> IndividualParty by using the Verify library
    • What do you think about it ?

Integration Tests with Verify

  • Create a Controller containing a GET method returning IndividualParties
    • Hardcoded once by using DataBuilder (Capone / Mesrine)
    • Check its behavior by using "classical" assertions
    • Check it with Verify
    • Compare the effort needed in both cases
    • Discuss the pros and cons of those 2 approaches

Non deterministic data

  • Create a new Controller containing a GET method returning Montana
    • How do you handle non-deterministic data in your tests ?
    • Use Verify to check your API result

Refactor legacy code

We have an improvable piece of code in our code base :

public static Template FindTemplateFor(string documentType, string recordType)
{
    foreach (var dtt in TemplateMappings())
    {
        if (dtt.DocumentType.ToString().Equals(documentType, StringComparison.InvariantCultureIgnoreCase) &&
            dtt.RecordType.ToString().Equals(recordType, StringComparison.InvariantCultureIgnoreCase))
        {
            return dtt;
        }
        else if (dtt.DocumentType.ToString()
                     .Equals(documentType, StringComparison.InvariantCultureIgnoreCase) &&
                 dtt.RecordType.ToString().Equals("ALL"))
        {
            return dtt;
        }
    }

    throw new ArgumentException("Invalid Document template type or record type");
}

  • Before refactoring it we need to add some tests

    • Add at least 2 Test Cases : Successful one and an Edge Case

  • Let's use the power of ApprovalTesting to check all the possible combinations without effort

  • cheat sheet

    • Generate combinations and have only 1 verified file