hosts file: Add a unit test that removes duplicated content

protokube/pkg/gossip/dns/hosts/BUILD.bazel

@@ -1,4 +1,4 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 
 go_library(
     name = "go_default_library",
@@ -7,3 +7,10 @@ go_library(
     visibility = ["//visibility:public"],
     deps = ["//vendor/github.com/golang/glog:go_default_library"],
 )
+
+go_test(
+    name = "go_default_test",
+    srcs = ["hosts_test.go"],
+    embed = [":go_default_library"],
+    deps = ["//pkg/diff:go_default_library"],
+)

protokube/pkg/gossip/dns/hosts/hosts_test.go

@@ -0,0 +1,109 @@
+/*
+Copyright 2019 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 hosts
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"k8s.io/kops/pkg/diff"
+)
+
+func TestRemovesDuplicateGuardedBlocks(t *testing.T) {
+	in := `
+foo 1.2.3.4
+
+# Begin host entries managed by etcd-manager[etcd] - do not edit
+# End host entries managed by etcd-manager[etcd]
+# Begin host entries managed by etcd-manager[etcd] - do not edit
+# End host entries managed by etcd-manager[etcd]
+# Begin host entries managed by kops - do not edit
+# End host entries managed by kops
+# Begin host entries managed by kops - do not edit
+# End host entries managed by kops
+# Begin host entries managed by kops - do not edit
+# End host entries managed by kops
+# Begin host entries managed by kops - do not edit
+# End host entries managed by kops
+# Begin host entries managed by kops - do not edit
+# End host entries managed by kops
+# Begin host entries managed by kops - do not edit
+# End host entries managed by kops
+# Begin host entries managed by kops - do not edit
+# End host entries managed by kops
+# Begin host entries managed by kops - do not edit
+# End host entries managed by kops
+`
+
+	expected := `
+foo 1.2.3.4
+
+# Begin host entries managed by etcd-manager[etcd] - do not edit
+# End host entries managed by etcd-manager[etcd]
+# Begin host entries managed by etcd-manager[etcd] - do not edit
+# End host entries managed by etcd-manager[etcd]
+
+# Begin host entries managed by kops - do not edit
+a\t100.0.1.1 100.0.1.2
+b\t100.0.2.1
+c\t
+# End host entries managed by kops
+`
+
+	expected = strings.Replace(expected, "\\t", "\t", -1)
+
+	dir, err := ioutil.TempDir("", "")
+	if err != nil {
+		t.Fatalf("error creating temp dir: %v", err)
+	}
+	defer func() {
+		err := os.RemoveAll(dir)
+		if err != nil {
+			t.Errorf("failed to remove temp dir %q: %v", dir, err)
+		}
+	}()
+
+	p := filepath.Join(dir, "hosts")
+	addrToHosts := map[string][]string{
+		"a": {"100.0.1.2", "100.0.1.1"},
+		"b": {"100.0.2.1"},
+		"c": {},
+	}
+
+	if err := ioutil.WriteFile(p, []byte(in), 0755); err != nil {
+		t.Fatalf("error writing hosts file: %v", err)
+	}
+
+	if err := UpdateHostsFileWithRecords(p, addrToHosts); err != nil {
+		t.Fatalf("error updating hosts file: %v", err)
+	}
+
+	b, err := ioutil.ReadFile(p)
+	if err != nil {
+		t.Fatalf("error reading output file: %v", err)
+	}
+
+	actual := string(b)
+	if actual != expected {
+		diffString := diff.FormatDiff(expected, actual)
+		t.Logf("diff:\n%s\n", diffString)
+		t.Errorf("unexpected output.  expected=%q, actual=%q", expected, actual)
+	}
+}