Add unit tests for kubelet cadvisor_linux

This adds unit tests for kubelet cadvisor_linux.

pkg/kubelet/cadvisor/cadvisor_linux_test.go

@@ -0,0 +1,66 @@
+// +build linux
+
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cadvisor
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	cadvisorfs "github.com/google/cadvisor/fs"
+	"k8s.io/kubernetes/pkg/kubelet/types"
+)
+
+func TestImageFsInfoLabel(t *testing.T) {
+	testcases := []struct {
+		description     string
+		runtime         string
+		runtimeEndpoint string
+		expectedLabel   string
+		expectedError   error
+	}{{
+		description:     "LabelDockerImages should be returned",
+		runtime:         types.DockerContainerRuntime,
+		runtimeEndpoint: "",
+		expectedLabel:   cadvisorfs.LabelDockerImages,
+		expectedError:   nil,
+	}, {
+		description:     "LabelCrioImages should be returned",
+		runtime:         types.RemoteContainerRuntime,
+		runtimeEndpoint: CrioSocket,
+		expectedLabel:   cadvisorfs.LabelCrioImages,
+		expectedError:   nil,
+	}, {
+		description:     "Cannot find valid imagefs label",
+		runtime:         "invalid-runtime",
+		runtimeEndpoint: "",
+		expectedLabel:   "",
+		expectedError:   fmt.Errorf("no imagefs label for configured runtime"),
+	}}
+
+	for _, tc := range testcases {
+		t.Run(tc.description, func(t *testing.T) {
+			infoProvider := NewImageFsInfoProvider(tc.runtime, tc.runtimeEndpoint)
+			label, err := infoProvider.ImageFsInfoLabel()
+			assert.Equal(t, tc.expectedLabel, label)
+			assert.Equal(t, tc.expectedError, err)
+		})
+	}
+}