<p>We can use an interface (protocol) for many different reasons - being able to swap out the concrete object used for a mock is one of them - it allows us to isolate the unit being tested; 
eg for a VM that uses a bunch of services we don't want to test the Service or API layer, we want to see how the VM behaves when it's given certain data. </p>
<p>If a model is just a bunch of values like a simple struct, we get no benefit from hiding it behind an interface.</p>


We can use an interface (protocol) for many different reasons - being able to swap out the concrete object used for a mock is one of them - it allows us to isolate the unit being tested; 
eg for a VM that uses a bunch of services we don't want to test the Service or API layer, we want to see how the VM behaves when it's given certain data. 

If a model is just a bunch of values like a simple struct, we get no benefit from hiding it behind an interface.

When to use a protocol

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Before making the switch to development, I was a strategist and GM in the tech space.
