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>

README.md

@@ -184,6 +184,16 @@ matches some expectation:
       `ConditionType` should have
     * `reason` which is the exact string that should be present in the
       `Condition` with the `ConditionType`
+* `assert.placement`: (optional) an object describing assertions to make about
+  the placement (scheduling outcome) of Pods returned in the `kube.get` result.
+* `assert.placement.spread`: (optional) an single string or array of strings
+  for topology keys that the Pods returned in the `kube.get` result should be
+  spread evenly across, e.g. `topology.kubernetes.io/zone` or
+  `kubernetes.io/hostname`.
+* `assert.placement.pack`: (optional) an single string or array of strings for
+  topology keys that the Pods returned in the `kube.get` result should be
+  bin-packed within, e.g. `topology.kubernetes.io/zone` or
+  `kubernetes.io/hostname`.
 * `assert.json`: (optional) object describing the assertions to make about
   resource(s) returned from the `kube.get` call to the Kubernetes API server.
 * `assert.json.len`: (optional) integer representing the number of bytes in the
@@ -450,6 +460,102 @@ tests:
          reason: NewReplicaSetAvailable
 ```
 
+### Asserting scheduling outcomes using `assert.placement`
+
+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.
+
+#### Asserting even spread of Pods across a topology
+
+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.
+
+#### Asserting bin-packing of Pods
+
+Suppose you have configured your Kubernetes scheduler to bin-pack Pods onto
+hosts by scheduling Pods to hosts with the most allocated CPU resources:
+
+```yaml
+apiVersion: kubescheduler.config.k8s.io/v1
+kind: KubeSchedulerConfiguration
+profiles:
+- pluginConfig:
+  - args:
+      scoringStrategy:
+        resources:
+        - name: cpu
+          weight: 100
+        type: MostAllocated
+    name: NodeResourcesFit
+```
+
+You can create a `gdt-kube` test case that verifies that your `nginx`
+Deployment's Pods are packed onto the fewest unique hosts:
+
+```yaml
+tests:
+ - kube:
+     get: deployments/nginx
+   assert:
+     placement:
+       pack: kubernetes.io/hostname
+```
+
+`gdt-kube` will examine the total number of hosts that meet the nginx
+Deployment's scheduling and resource constraints and then assert that the
+number of hosts the Deployment's Pods landed on is the minimum number that
+would fit the total requested resources.
+
 ### Asserting resource fields using `assert.json`
 
 The `assert.json` field of a `gdt-kube` test Spec allows a test author to

action.go

@@ -100,7 +100,7 @@ func (a *Action) Do(
 ) error {
 	cmd := a.getCommand()
 
-	debug.Println(ctx, t, "kube: %s [ns: %s]", cmd, ns)
+	debug.Println(ctx, "kube: %s [ns: %s]", cmd, ns)
 	switch cmd {
 	case "get":
 		return a.get(ctx, t, c, ns, out)

assertions.go

@@ -5,6 +5,7 @@
 package kube
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -158,6 +159,8 @@ type Expect struct {
 	//            reason: NewReplicaSetAvailable
 	// ```
 	Conditions map[string]*ConditionMatch `yaml:"conditions,omitempty"`
+	// Placement describes expected Pod scheduling spread or pack outcomes.
+	Placement *PlacementAssertion `yaml:"placement,omitempty"`
 }
 
 // conditionMatch is a struct with fields that we will match a resource's
@@ -196,8 +199,21 @@ func (m *ConditionMatch) UnmarshalYAML(node *yaml.Node) error {
 	return nil
 }
 
+// PlacementAssertion describes an expectation for Pod scheduling outcomes.
+type PlacementAssertion struct {
+	// Spread contains zero or more topology keys that gdt-kube will assert an
+	// even spread across.
+	Spread *gdttypes.FlexStrings `yaml:"spread,omitempty"`
+	// Pack contains zero or more topology keys that gdt-kube will assert
+	// bin-packing of resources within.
+	Pack *gdttypes.FlexStrings `yaml:"pack,omitempty"`
+}
+
 // assertions contains all assertions made for the exec test
 type assertions struct {
+	// c is the connection to the Kubernetes API for when the assertions needs
+	// to query for things like placement outcomes or Node resources.
+	c *connection
 	// failures contains the set of error messages for failed assertions
 	failures []error
 	// exp contains the expected conditions to assert against
@@ -226,7 +242,7 @@ func (a *assertions) Failures() []error {
 
 // OK checks all the assertions against the supplied arguments and returns true
 // if all assertions pass.
-func (a *assertions) OK() bool {
+func (a *assertions) OK(ctx context.Context) bool {
 	exp := a.exp
 	if exp == nil {
 		if a.err != nil {
@@ -247,7 +263,10 @@ func (a *assertions) OK() bool {
 	if !a.conditionsOK() {
 		return false
 	}
-	if !a.jsonOK() {
+	if !a.jsonOK(ctx) {
+		return false
+	}
+	if !a.placementOK(ctx) {
 		return false
 	}
 	return true
@@ -426,7 +445,7 @@ func (a *assertions) conditionsOK() bool {
 
 // jsonOK returns true if the subject matches the JSON conditions, false
 // otherwise
-func (a *assertions) jsonOK() bool {
+func (a *assertions) jsonOK(ctx context.Context) bool {
 	exp := a.exp
 	if exp.JSON != nil && a.hasSubject() {
 		var err error
@@ -438,7 +457,7 @@ func (a *assertions) jsonOK() bool {
 			}
 		}
 		ja := gdtjson.New(exp.JSON, b)
-		if !ja.OK() {
+		if !ja.OK(ctx) {
 			for _, f := range ja.Failures() {
 				a.Fail(f)
 			}
@@ -448,6 +467,29 @@ func (a *assertions) jsonOK() bool {
 	return true
 }
 
+// placementOK returns true if the subject matches the Placement conditions,
+// false otherwise
+func (a *assertions) placementOK(ctx context.Context) bool {
+	exp := a.exp
+	if exp.Placement != nil && a.hasSubject() {
+		// TODO(jaypipes): Handle list returns...
+		res, ok := a.r.(*unstructured.Unstructured)
+		if !ok {
+			panic("expected result to be unstructured.Unstructured")
+		}
+		spread := exp.Placement.Spread
+		if spread != nil {
+			ok = a.placementSpreadOK(ctx, res, spread.Values())
+		}
+		pack := exp.Placement.Pack
+		if pack != nil {
+			ok = ok && a.placementPackOK(ctx, res, pack.Values())
+		}
+		return ok
+	}
+	return true
+}
+
 // hasSubject returns true if the assertions `r` field (which contains the
 // subject of which we inspect) is not `nil`.
 func (a *assertions) hasSubject() bool {
@@ -465,11 +507,13 @@ func (a *assertions) hasSubject() bool {
 // newAssertions returns an assertions object populated with the supplied http
 // spec assertions
 func newAssertions(
+	c *connection,
 	exp *Expect,
 	err error,
 	r interface{},
 ) gdttypes.Assertions {
 	return &assertions{
+		c:        c,
 		failures: []error{},
 		exp:      exp,
 		err:      err,

connect.go

@@ -7,6 +7,7 @@ package kube
 import (
 	"context"
 	"fmt"
+	"os"
 
 	gdtcontext "github.com/gdt-dev/gdt/context"
 	"k8s.io/apimachinery/pkg/api/meta"
@@ -191,7 +192,7 @@ func (s *Spec) connect(ctx context.Context) (*connection, error) {
 	}
 	disco := discocached.NewMemCacheClient(discoverer)
 	mapper := restmapper.NewDeferredDiscoveryRESTMapper(disco)
-	expander := restmapper.NewShortcutExpander(mapper, disco)
+	expander := restmapper.NewShortcutExpander(mapper, disco, func(s string) { fmt.Fprint(os.Stderr, s) })
 
 	return &connection{
 		mapper: expander,

eval.go

@@ -65,10 +65,10 @@ func (s *Spec) Eval(ctx context.Context, t *testing.T) *result.Result {
 				return result.New(result.WithRuntimeError(err))
 			}
 		}
-		a = newAssertions(s.Assert, err, out)
-		success = a.OK()
+		a = newAssertions(c, s.Assert, err, out)
+		success = a.OK(ctx)
 		debug.Println(
-			ctx, t, "%s (try %d after %s) ok: %v",
+			ctx, "%s (try %d after %s) ok: %v",
 			s.Title(), attempts, after, success,
 		)
 		if success {
@@ -77,7 +77,7 @@ func (s *Spec) Eval(ctx context.Context, t *testing.T) *result.Result {
 		}
 		for _, f := range a.Failures() {
 			debug.Println(
-				ctx, t, "%s (try %d after %s) failure: %s",
+				ctx, "%s (try %d after %s) failure: %s",
 				s.Title(), attempts, after, f,
 			)
 		}