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I guess your mocks return null which causes this error. You’d have to actually implement `IMocks`.

thank you for a quick reply. I will try that.

I implemented IMocks, as you said. It worked. Now that I want to test kubernetes namspaces (only) I would have to create a separate test stack with kubernetes and kubernetese namspaces.
It feels a bit clumbersome, but it works.
I can live with that.

To anyone else reading this. the solution here is to set up IMocks with
```var mocks = new Mock&lt;IMocks&gt;();

            mocks.Setup(m =&gt; m.NewResourceAsync(It.IsAny&lt;string&gt;(), It.IsAny&lt;string&gt;(),
                    It.IsAny&lt;ImmutableDictionary&lt;string, object&gt;&gt;(), It.IsAny&lt;string&gt;(), It.IsAny&lt;string&gt;()))
                .ReturnsAsync((string type, string name, ImmutableDictionary&lt;string, object&gt; inputs, string provider,
                    string id) =&gt; (name + "_id", inputs));```