Fixes unit tests indeterminism (#6496)

We were getting sporadic coverage differences on `controller/k8s/test_helper.go` and `pkg/healthcheck/healthcheck_test.go` on pushes unrelated to those files.

For the former, the problem was in tests in `controller/k8s/api_test.go` that compared slices of pods and services by sorting them. The `Sort` interface was implemented through the methods in `test_helper.go`. There is indeterminism in that sorting at the go library level apparently, in that the `Swap` method is not always called, which impacted the coverage report. The fix consists on comparing those slices item by item without needing to sort beforehand.

As for `healthcheck_test.go`, `validateControlPlanePods()` in `healthcheck.go` short-circuits on the first pod having all its containers ready. The unit tests iterate over maps, an iteration we know is not deterministic, so sometimes the short-circuiting avoided to ever cover the `!container.Ready` block, thus affecting the coverage report. This is fixed by adding a new small test that makes sure that block is covered.

controller/k8s/api_test.go

@@ -5,7 +5,6 @@ import (
 	"errors"
 	"fmt"
 	"reflect"
-	"sort"
 	"testing"
 
 	"k8s.io/apimachinery/pkg/labels"
@@ -942,11 +941,22 @@ status:
 				t.Fatalf("api.GetPodsFor() unexpected error, expected [%s] got: [%s]", exp.err, err)
 			}
 
-			sort.Sort(byPod(pods))
-			sort.Sort(byPod(k8sResultPods))
-			if !reflect.DeepEqual(pods, k8sResultPods) {
+			if len(pods) != len(k8sResultPods) {
 				t.Fatalf("Expected: %+v, Got: %+v", k8sResultPods, pods)
 			}
+
+			for _, pod := range pods {
+				found := false
+				for _, resultPod := range k8sResultPods {
+					if reflect.DeepEqual(pod, resultPod) {
+						found = true
+						break
+					}
+				}
+				if !found {
+					t.Fatalf("Expected: %+v, Got: %+v", k8sResultPods, pods)
+				}
+			}
 		}
 	})
 }
@@ -1348,11 +1358,22 @@ spec:
 				t.Fatalf("api.GetServicesFor() unexpected error, expected [%s] got: [%s]", exp.err, err)
 			}
 
-			sort.Sort(byService(k8sResultServices))
-			sort.Sort(byService(services))
-			if !reflect.DeepEqual(services, k8sResultServices) {
+			if len(services) != len(k8sResultServices) {
 				t.Fatalf("Expected: %+v, Got: %+v", k8sResultServices, services)
 			}
+
+			for _, service := range services {
+				found := false
+				for _, resultService := range k8sResultServices {
+					if reflect.DeepEqual(service, resultService) {
+						found = true
+						break
+					}
+				}
+				if !found {
+					t.Fatalf("Expected: %+v, Got: %+v", k8sResultServices, services)
+				}
+			}
 		}
 
 	})

controller/k8s/test_helper.go

@@ -2,7 +2,6 @@ package k8s
 
 import (
 	"github.com/linkerd/linkerd2/pkg/k8s"
-	corev1 "k8s.io/api/core/v1"
 )
 
 // NewFakeAPI provides a mock Kubernetes API for testing.
@@ -35,15 +34,3 @@ func NewFakeAPI(configs ...string) (*API, error) {
 		ES,
 	), nil
 }
-
-type byPod []*corev1.Pod
-
-func (bp byPod) Len() int           { return len(bp) }
-func (bp byPod) Swap(i, j int)      { bp[i], bp[j] = bp[j], bp[i] }
-func (bp byPod) Less(i, j int) bool { return bp[i].Name <= bp[j].Name }
-
-type byService []*corev1.Service
-
-func (bs byService) Len() int           { return len(bs) }
-func (bs byService) Swap(i, j int)      { bs[i], bs[j] = bs[j], bs[i] }
-func (bs byService) Less(i, j int) bool { return bs[i].Name <= bs[j].Name }

pkg/healthcheck/healthcheck_test.go

@@ -1462,6 +1462,18 @@ func TestValidateControlPlanePods(t *testing.T) {
 		}
 	})
 
+	// This test is just for ensuring full coverage of the validateControlPlanePods function
+	t.Run("Returns an error if the only pod is not ready", func(t *testing.T) {
+		pods := []corev1.Pod{
+			pod("linkerd-proxy-injector-5f79ff4844-", corev1.PodRunning, false),
+		}
+
+		err := validateControlPlanePods(pods)
+		if err == nil {
+			t.Fatal("Expected error, got nothing")
+		}
+	})
+
 	t.Run("Returns nil if, HA mode, at least one pod of each control plane component is ready", func(t *testing.T) {
 		pods := []corev1.Pod{
 			pod("linkerd-destination-9843948665-48082", corev1.PodRunning, true),