add simple tests for entry writing

etchosts_test.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+)
+
+func Test_writeEntryWithBanner(t *testing.T) {
+	type args struct {
+		ip    string
+		names []string
+	}
+	tests := []struct {
+		name    string
+		args    args
+		wantTmp string
+		wantErr bool
+	}{
+		{"do not write empty ip", args{"", []string{"somename", "someothername"}}, "", false},
+		{"do not write empty names", args{"1.2.3.4", []string{}}, "", false},
+		{"complete entry", args{"1.2.3.4", []string{"somename", "someothername"}}, fmt.Sprintf("%s\n1.2.3.4\tsomename someothername\n", banner), false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tmp := &bytes.Buffer{}
+			if err := writeEntryWithBanner(tmp, tt.args.ip, tt.args.names); (err != nil) != tt.wantErr {
+				t.Errorf("writeEntryWithBanner() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if gotTmp := tmp.String(); gotTmp != tt.wantTmp {
+				t.Errorf("writeEntryWithBanner() got:\n%#v, want\n%#v", gotTmp, tt.wantTmp)
+			}
+		})
+	}
+}