如何测试使用Activator.CreateInstance（…）的方法？

Question

I'm writing a test for the following method:

public IAnInterface Instantiator()
{
    var type = Type.GetType(A_CONSTANT_STRING);
    return (IAnInterface)Activator.CreateInstance(type);
}

When the test is running, the type obtained from the Type.GetType(...) method is null. My questions are:

1. The null is being returned because not all the types are loaded(?) when the tests are executed?
2. How to overcome this problem? Actually I want to test if the required type has been returned.

Thanks in advance

Answer 1

As @Krekkon already mentioned Type.GetType() method requires the following string:

The assembly-qualified name of the type to get. See AssemblyQualifiedName. If the type is in the currently executing assembly or in Mscorlib.dll, it is sufficient to supply the type name qualified by its namespace.

For question #2: You will not be able to test whether the type has been returned because of the static call to Type.GetType() . If you can change the code you could introduce an interface that is responsible for type resolving and represents a facades of the static GetType method call:

interface ITypeResolver
{
  Type GetType(string typeName);
}

class SomeClass
{
  private readonly ITypeResolver typeResolver = ...;

  public IAnInterface Instantiator()
  {
    var type = this.typeResolver.GetType(A_CONSTANT_STRING);
    return (IAnInterface)Activator.CreateInstance(type);
  }
}

Using an interface you are able to mock the ITypeResolver and also test the implementation of ITypeResolver interface in Isolation.

Answer 2

var type = Type.GetType("namespace.qualified.TypeName");

Answer 3

通过添加对在A_CONSTANT_STRING指定的类型所在的项目的引用来解决。

Answer 4

What assembly is your type defined in? Assuming your method is in the same assembly as the type you are looking for, try:

var type = Assembly.GetExecutingAssembly().GetTypes()
    .First(t => t.Name == A_CONSTANT_STRING);

return (IAnInterface)Activator.CreateInstance(type);