feat(test): add utilities for JSONPath-like access to unstructured Kubernetes objects

[manusa]

This PR adds test utility functions that provide JSONPath-like field access for unstructured.Unstructured objects.

The primary goal is to improve test assertion readability by replacing deeply-nested type assertions with clean, concise path-based field access.

Readability Improvement

Before:

s.Equal("quay.io/containerdisks/fedora:latest",
  decodedResult[0].Object["spec"].(map[string]interface{})["template"].(map[string]interface{})["spec"].(map[string]interface{})["volumes"].([]interface{})[0].(map[string]interface{})["containerDisk"].(map[string]interface{})["image"].(string),
  "invalid default image")

After:

s.Equal("quay.io/containerdisks/fedora:latest",
  test.FieldString(vm, "spec.template.spec.volumes[0].containerDisk.image"),
  "invalid default image")

[Cali0707]

@manusa I think you still need a nil check on val here as well

[Cali0707]

@manusa I'm not 100% sure this behaviour is ideal - there could be scenarios where I'm testing and expecting to receive a value of 0 - for example status.replicas. How would we be able to distinguish between the value actually being 0 vs. not being set/not being an int?

Or do you think that's fine because this is for tests? In that case I'm fine with it but let's add a note in the docstring about ensuring that you don't assert expecting an actual value to be 0

[manusa]

For that purpose you would use test.FieldExists(vm, "spec.instancetype") and expect it to be false

https://github.com/marcnuri-forks/kubernetes-mcp-server/blob/8e5f6df7d009ebb7785c12d46faed9e73048be23/pkg/mcp/kubevirt_test.go#L283

[manusa]

I'll need to revisit for this case for the expecting to be 0

[Cali0707]

Same as my comment about FieldInt - it would be nice to be able to tell the difference between not set and set to ""

[manusa]

For that purpose you would use test.FieldExists(vm, "spec.instancetype") and expect it to be false

https://github.com/marcnuri-forks/kubernetes-mcp-server/blob/8e5f6df7d009ebb7785c12d46faed9e73048be23/pkg/mcp/kubevirt_test.go#L283

[manusa]

I've added the nil-check.
For the other cases you mention, this is not an easy solution.
The goal of the utility is to make the tests more readable.
Any solution I can think of would defeat the purpose of these functions.

For the edge cases you mention, there is both Field, FieldValue and FieldExists` functions that can be leveraged to perform the extra assertion.
Any of these can be used to perform the extra checks that ensure that a field exists and contains an empty string as opposed to a nil value or a 0 int as opposed to a nil field value.

I've added some godoc to the simplified accessors so that users are aware of the limitation.

[Cali0707]

LGTM, thanks @manusa

The tests are way more readable now 😄