diff --git a/pkg/healthcheck/sidecar_test.go b/pkg/healthcheck/sidecar_test.go
new file mode 100644
index 000000000..2824b8ad3
--- /dev/null
+++ b/pkg/healthcheck/sidecar_test.go
@@ -0,0 +1,122 @@
+package healthcheck
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/linkerd/linkerd2/pkg/k8s"
+	corev1 "k8s.io/api/core/v1"
+)
+
+func TestHasExistingSidecars(t *testing.T) {
+	for _, tc := range []struct {
+		podSpec  *corev1.PodSpec
+		expected bool
+	}{
+		{
+			podSpec:  &corev1.PodSpec{},
+			expected: false,
+		},
+		{
+			podSpec: &corev1.PodSpec{
+				Containers: []corev1.Container{
+					{
+						Name:  "foo",
+						Image: "bar",
+					},
+				},
+				InitContainers: []corev1.Container{
+					{
+						Name:  "foo",
+						Image: "bar",
+					},
+				},
+			},
+			expected: false,
+		},
+		{
+			podSpec: &corev1.PodSpec{
+				Containers: []corev1.Container{
+					{
+						Name: k8s.ProxyContainerName,
+					},
+				},
+			},
+			expected: true,
+		},
+		{
+			podSpec: &corev1.PodSpec{
+				Containers: []corev1.Container{
+					{
+						Name: "istio-proxy",
+					},
+				},
+			},
+			expected: true,
+		},
+		{
+			podSpec: &corev1.PodSpec{
+				Containers: []corev1.Container{
+					{
+						Image: "ghcr.io/linkerd/proxy:1.0.0",
+					},
+				},
+			},
+			expected: true,
+		},
+		{
+			podSpec: &corev1.PodSpec{
+				Containers: []corev1.Container{
+					{
+						Image: "gcr.io/istio-release/proxyv2:1.0.0",
+					},
+				},
+			},
+			expected: true,
+		},
+		{
+			podSpec: &corev1.PodSpec{
+				InitContainers: []corev1.Container{
+					{
+						Name: "linkerd-init",
+					},
+				},
+			},
+			expected: true,
+		},
+		{
+			podSpec: &corev1.PodSpec{
+				InitContainers: []corev1.Container{
+					{
+						Name: "istio-init",
+					},
+				},
+			},
+			expected: true,
+		},
+		{
+			podSpec: &corev1.PodSpec{
+				InitContainers: []corev1.Container{
+					{
+						Image: "ghcr.io/linkerd/proxy-init:1.0.0",
+					},
+				},
+			},
+			expected: true,
+		},
+		{
+			podSpec: &corev1.PodSpec{
+				InitContainers: []corev1.Container{
+					{
+						Image: "gcr.io/istio-release/proxy_init:1.0.0",
+					},
+				},
+			},
+			expected: true,
+		},
+	} {
+		if !reflect.DeepEqual(HasExistingSidecars(tc.podSpec), tc.expected) {
+			t.Errorf("expected: %v, got: %v", tc.expected, HasExistingSidecars(tc.podSpec))
+		}
+	}
+}