Implement lab05 stringer for anz-bank go-course

Update test to fix newline issue

05_stringer/undrewb/main.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+var out io.Writer = os.Stdout
+
+type IPAddr [4]byte
+
+func (ip IPAddr) String() string {
+	return fmt.Sprintf("%v.%v.%v.%v", ip[0], ip[1], ip[2], ip[3])
+}
+
+func main() {
+	fmt.Fprintln(out, IPAddr{127, 0, 0, 1})
+}

05_stringer/undrewb/main_test.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMainOutput(t *testing.T) {
+	var buf bytes.Buffer
+	out = &buf
+
+	main()
+
+	want := strconv.Quote("127.0.0.1\n")
+	got := strconv.Quote(buf.String())
+
+	assert.Equal(t, got, want)
+}
+
+var stringerData = []struct {
+	name  string
+	input IPAddr
+	want  string
+}{
+	{name: "localhost",
+		input: IPAddr{127, 0, 0, 1},
+		want:  "127.0.0.1"},
+	{name: "four octet addr",
+		input: IPAddr{68, 2, 44, 125},
+		want:  "68.2.44.125"},
+	{name: "three octet addr",
+		input: IPAddr{68, 2, 125},
+		want:  "68.2.125.0"},
+	{name: "two octet addr",
+		input: IPAddr{9, 5},
+		want:  "9.5.0.0"},
+	{name: "one octet addr",
+		input: IPAddr{144},
+		want:  "144.0.0.0"},
+	{name: "empty",
+		input: IPAddr{},
+		want:  "0.0.0.0"},
+}
+
+func TestStringer(t *testing.T) {
+	for _, tt := range stringerData {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			got := fmt.Sprint(tt.input)
+			assert.Equal(t, got, tt.want)
+		})
+	}
+}