How would I instantiate a VSTO add-in in a unit test project?-CodePudding

While instantiate a VSTO base class in my unit test project i have got Null Reference exception. Below is the code that i have used and snapshot of the error which i have got while debug the test.

public UnitTest1(): base(Globals.Factory.GetRibbonFactory())
    {
        
    }

This add-in is work on Visio Application and I am actually new to this add-in development and not familiar how would i unit test my code for the add-in.

CodePudding user response：

You cannot instantiate VSTO add-in in a Unit Test project. More precisely, you can, but it's hard. There are much easier ways, for example, you can extract the functionality from the VSTO-related classes to "clean" classes and instantiate them instead. For example, if you have:

public partial class ThisAddIn {
  public void Foo(Visio.Application app) { ... }
  public void Bar() {
    this.Foo(this.Application);
  }
}

You could go for something like this instead:

pulic class ThisAddinActions {
  public void Foo(Visio.Application app) { ... } 
}

public partial class ThisAddIn {
  public ThisAddinActions _actions = new ThisAddinActions();
  public void Bar() {
    _actions.Foo(this.Application);
  }
}

//// test 

[TestClass]
public class UnitTest1 {
  [TestMethod]
  public void TestMethod1() {
    var app = new Visio.Application()
    var actions = new ThisAddinActions();
    actions.Foo(app);
  }
}

CodePudding user response：

Instantiating an add-in instance (or the ribbon part) is not really a good idea. Consider refactoring the add-in in the way that separate methods can be tested in unit tests with mocked dependencies.

There are several aspects here. You may consider the following:

Introducing any mocking library, so you could mock dependencies.
Use the dependency injection mechanisms to avoid direct dependencies and to be able to apply unit tests to the code without a question.

You may find a lot of existing threads there such as: