Mocking generic protected methods

[esegura]

Hi folks,

I'm trying to test my EntityFramework DbContext object. I wonder if
this is possible:


mockA.Protected().Setup<IDbSet<IEntity>>("GetSet").Returns(mockDbSet.Object).Verifiable();

where A looks like this:

public class A : DbContext{
public void Save<T>(T entity) where T : class, IEntity
{
this.GetSet<T>().Add(entity);
}

protected virtual IDbSet<T> GetSet<T>() where T : class,
IEntity
{
return this.Set<T>();
}
}

If I just do that, I get this exception:

at System.Linq.Expressions.Expression.ValidateMethodInfo(MethodInfo
method)
at System.Linq.Expressions.Expression.Call(Expression instance,
MethodInfo method, IEnumerable`1 arguments)
at Moq.Protected.ProtectedMock`1.GetMethodCall[TResult](MethodInfo
method, Object[] args)
at Moq.Protected.ProtectedMock`1.Setup[TResult](String methodName,
Object[] args)
at xyz.SaveTest() in C:\xyz.cs:line 79.

Looking at the source, it seems that we could use a new overload of
the ProtectedMock.GetMethodCall() method, one that calls a different
overload of Expression.Call(), the one with type arguments. Maybe
something like this:

private static Expression<Func<T, TResult>>
GetMethodCall<TResult>(MethodInfo method, Type[] typeArguments,
object[] args)
{
var param = Expression.Parameter(typeof(T), "mock");
return Expression.Lambda<Func<T, TResult>>(Expression.Call(param,
method, typeArguments, ToExpressionArgs(args)), param);
}

Would that work? Or there is another way to do it and I completely
missed it?
Thanks!
-e

[esegura]

-bump


Any thoughts on this? I mean, even if all I get is 'you are doing it
wrong' kind :)

[Daniel Cazzulino]

Testing a DbContext seems wrong, as you'd be testing EF itself? (it's like creating a test for system.string and trying to override stuff there ;)). 

This might be useful: http://blogs.clariusconsulting.net/kzu/how-to-design-a-unit-testable-domain-model-with-entity-framework-code-first/

/kzu

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Daniel Cazzulino | Developer Lead | XML MVP | Clarius Consulting | +1 425.329.3471

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[esegura]

Hi Daniel,

Thanks for replying.

I'm not trying to unit test DbContext, no. I'm just trying to unit
test my code, the code in class 'A'.
But yes, after I posted that question I realized it could be
misleading. Let me try to clarify.
(I actually used that very blog post of yours to model my code)

I guess the problem was with my phrasing of the problem. Note that I
used the word "_my_" (DbContext) to refer to the class under test:
'A' (which extends from DbContext)


If you compare the code in your post:
internal class DomainContext : DbContext, IDomainContext
{
public void Save<T>(T entity) where T : IEntity
{ this.Set<T>().Add(entity); }
}

with my code above, I'm sure you will see that they look alike :):

public class A : DbContext{
public void Save<T>(T entity) where T : class, IEntity
{ this.GetSet<T>().Add(entity); }
protected virtual IDbSet<T> GetSet<T>() where T :
class,IEntity { return this.Set<T>(); }
}

So, now that that's out of the way, let me rephrase what I'm trying to
achieve: I want to mock 'GetSet()' so I can Assert that the Add()
method of the IDbSet has been called. But GetSet() is generic, thus my
question:

Is it possible to mock a protected generic method?

Thanks,
Eduardo

On Oct 7, 7:00 am, Daniel Cazzulino <dan...@cazzulino.com> wrote:
> Testing a DbContext seems wrong, as you'd be testing EF itself? (it's like
> creating a test for system.string and trying to override stuff there ;)).
>

> This might be useful:http://blogs.clariusconsulting.net/kzu/how-to-design-a-unit-testable-...

[Daniel Cazzulino]

you're testing the DbContext still. Your derived DbContext will typically have NO logic whatesoever (haven't seen a case where that would be needed).

and testing your DbContext-derived class can only make sense if it actually works against a real database, so, more of an integration test. 

/kzu

--
Daniel Cazzulino | Developer Lead | XML MVP | Clarius Consulting | +1 425.329.3471