Unit testing a Powershell Azure Function App?

I have an Azure Function written in Powershell:

function Invoke {
    param($Request)
    Push-OutputBinding -Name Response -Value ([HttpResponseContext]@{
        StatusCode = [HttpStatusCode]::OK
        Body       = "Hello!"
    })
}

I have a Pester unit test for this function:

Describe "Invoke" {
    It "Returns a 200 response" {
        $Response = Invoke -Request [HttpRequestContext]@{}
        $Response.StatusCode | Should Be ([HttpStatusCode]::OK)
    }
}

Running this test yields:

Describing Invoke
  [-] Returns a 200 response 4ms (3ms|1ms)
   RuntimeException: Unable to find type [HttpRequestContext].

Presumably the PowerShellWorker injects these types when it runs the script and so they are not available when Pester invokes the test. In falling order of desirability, how can I:

1. Import these types in my test run? For example, is there a module I could import?
2. Inject mocks of these types? Pester has support for creating mocks of objects, but not inject types?
3. Ask the PowerShellWorker to invoke the function from my test? (I could probably invoke func host start and write integration tests instead, but I would really prefer to have unit tests if possible.)

I'd appreciate any lead that can help me with this.

UPDATE: As pointed out in comments, I had deleted a param() when compacting my example. To clarify, the idea is to support type annotations in both test and production code.

UPDATE2: Corrected spelling as per mclayton's suggestion.

I've not seen a really concise approach to unit testing PowerShell Azure Functions....or at least they certainly get less love than C#/Javascript/Python in general.

You can however mock the type in pester using New-MockObject

I've also seen ways of using entryPoints to run a script and then test the script independently of your Azure Function so you don't have to rely on the worker runtime at all but how deep down the rabbit hole do you want to go?!

I just ran into this today, and I solved it by moving the using statement in run.ps1 to the top of the profile.ps1 file, and adding a mock type to the unit tests in the BeforeEach, before dot-sourcing run.ps1:

enum HttpStatusCode {
    OK
    InternalServerError
}
class HttpResponseContext {
    [HttpStatusCode]$StatusCode
    [string]$ContentType
    [string]$Body
}
function Push-OutputBinding($Name, $Value) {}

Worked like a charm for me.