Mocking Resources in Tests

[rohan-datar]

I have a module that reads a bunch of resources from the environment and performs some validation on them. This module is imported by other modules that use the resources as needed. When writing tests for my modules, I'd like to mock the values provided by the resource module. As far as I can tell, Pkl does not have a simple way to do this. Any suggestions on how I can achieve this?

// resources.pkl
const envVal = read("env:ENV_VAL")

const envValValidated = if (envVal.toInt() > 0) envVal else throw("bad value")

// foo.pkl
import "resources.pkl"
bar = envVal + 5

I'd like to be able to write an example test like this:

// foo_test.pkl
amends "pkl:test"
import "foo.pkl" as foo

examples {
   ["foo"] {
       foo.output.text
   }
}

If I run this test in an environment where ENV_VAL is not set or has an invalid value, it will fail, it will also fail if ENV_VAL changes even if my module code is unchanged. Ideally I'd be able to set the value in foo_test.pkl so I don't have to worry about it, but it's unclear how I would do that in this case.

[rohan-datar]

I got around this by using an import expression rather than a clause in foo.pkl and then amended foo after it was imported in foo_test

// foo.pkl
resources = import("resources.pkl")
...

//  foo_test.pkl
import "foo.pkl" as foo
import "resources.pkl" as r
local fooWithMockedResources = (foo) {
    resources = new r {
       envValValidated = 20
   }
}
examples {
   ["foo"] {
       fooWithMockedResources.output.text
   }
}

However this exposes resources as a property within foo that modules that amend foo can directly modify. That would ideally not be the case.

[bioball]

Your solution here is what I'd suggest. You'll want to expose these values so they can be stubbed out within your tests.

This does mean that it becomes an exported API, but I don't really have a good workaround for that. This is a problem that you'd have in many other languages too.

By the way, you don't need to re-import resources. Also, your import "foo.pkl" as foo is redundant (the import already declares the same name).

import "foo.pkl"

local fooWithMockedResources = (foo) {
    resources = new {
       envValValidated = 20
   }
}

examples {
   ["foo"] {
       fooWithMockedResources.output.text
   }
}