Commits on Jun 1, 2024

1. add placement spread assertions …

   The `assert.placement` field of a `gdt-kube` test Spec allows a test author to
   specify the expected scheduling outcome for a set of Pods returned by the
   Kubernetes API server from the result of a `kube.get` call.
   
   Suppose you have a Deployment resource with a `TopologySpreadConstraints` that
   specifies the Pods in the Deployment must land on different hosts:
   
   ```yaml
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: nginx-deployment
     labels:
       app: nginx
   spec:
     replicas: 3
     selector:
       matchLabels:
         app: nginx
     template:
       metadata:
         labels:
           app: nginx
       spec:
         containers:
          - name: nginx
            image: nginx:latest
            ports:
             - containerPort: 80
         topologySpreadConstraints:
          - maxSkew: 1
            topologyKey: kubernetes.io/hostname
            whenUnsatisfiable: DoNotSchedule
            labelSelector:
              matchLabels:
                app: nginx
   ```
   
   You can create a `gdt-kube` test case that verifies that your `nginx`
   Deployment's Pods are evenly spread across all available hosts:
   
   ```yaml
   tests:
    - kube:
        get: deployments/nginx
      assert:
        placement:
          spread: kubernetes.io/hostname
   ```
   
   If there are more hosts than the `spec.replicas` in the Deployment, `gdt-kube`
   will ensure that each Pod landed on a unique host. If there are fewer hosts
   than the `spec.replicas` in the Deployment, `gdt-kube` will ensure that there
   is an even spread of Pods to hosts, with any host having no more than one more
   Pod than any other.
   
   Debug/trace output includes information on how the placement spread
   looked like to the gdt-kube placement spread asserter:
   
   ```
   jaypipes@lappie:~/src/github.com/gdt-dev/kube$ go test -v -run TestPlacementSpread ./eval_test.go
   === RUN   TestPlacementSpread
   === RUN   TestPlacementSpread/placement-spread
   [gdt] [placement-spread] kube: create [ns: default]
   [gdt] [placement-spread] create-deployment (try 1 after 1.254µs) ok: true
   [gdt] [placement-spread] using timeout of 40s (expected: false)
   [gdt] [placement-spread] kube: get [ns: default]
   [gdt] [placement-spread] deployment-ready (try 1 after 2.482µs) ok: false
   [gdt] [placement-spread] deployment-ready (try 1 after 2.482µs) failure: assertion failed: match field not equal: $.status.readyReplicas not present in subject
   [gdt] [placement-spread] kube: get [ns: default]
   [gdt] [placement-spread] deployment-ready (try 2 after 307.618472ms) ok: false
   [gdt] [placement-spread] deployment-ready (try 2 after 307.618472ms) failure: assertion failed: match field not equal: $.status.readyReplicas not present in subject
   [gdt] [placement-spread] kube: get [ns: default]
   [gdt] [placement-spread] deployment-ready (try 3 after 1.245091704s) ok: false
   [gdt] [placement-spread] deployment-ready (try 3 after 1.245091704s) failure: assertion failed: match field not equal: $.status.readyReplicas not present in subject
   [gdt] [placement-spread] kube: get [ns: default]
   [gdt] [placement-spread] deployment-ready (try 4 after 2.496969168s) ok: false
   [gdt] [placement-spread] deployment-ready (try 4 after 2.496969168s) failure: assertion failed: match field not equal: $.status.readyReplicas had different values. expected 6 but found 3
   [gdt] [placement-spread] kube: get [ns: default]
   [gdt] [placement-spread] deployment-ready (try 5 after 3.785007183s) ok: true
   [gdt] [placement-spread] kube: get [ns: default]
   [gdt] [placement-spread/assert-placement-spread] domain: topology.kubernetes.io/zone, unique nodes: 3
   [gdt] [placement-spread/assert-placement-spread] domain: topology.kubernetes.io/zone, pods per node: [2 2 2]
   [gdt] [placement-spread] deployment-spread-evenly-across-hosts (try 1 after 3.369µs) ok: true
   [gdt] [placement-spread] kube: delete [ns: default]
   [gdt] [placement-spread] delete-deployment (try 1 after 1.185µs) ok: true
   
   --- PASS: TestPlacementSpread (4.98s)
       --- PASS: TestPlacementSpread/placement-spread (4.96s)
   PASS
   ok  	command-line-arguments	4.993s
   ```
   
   Issue #7
   
   Signed-off-by: Jay Pipes <jaypipes@gmail.com>

   

   jaypipes committed Jun 1, 2024
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