Adding new simple test to relay package

Signed-off-by: Pedro Tanaka <pedro.tanaka@shopify.com>

go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/prometheus/client_golang v1.11.0
 	github.com/prometheus/client_model v0.2.0
 	github.com/prometheus/common v0.30.0
+	github.com/stvp/go-udp-testing v0.0.0-20201019212854-469649b16807
 	gopkg.in/alecthomas/kingpin.v2 v2.2.6
 	gopkg.in/yaml.v2 v2.4.0
 )

go.sum

@@ -190,6 +190,8 @@ github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXf
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/stvp/go-udp-testing v0.0.0-20201019212854-469649b16807 h1:LUsDduamlucuNnWcaTbXQ6aLILFcLXADpOzeEH3U+OI=
+github.com/stvp/go-udp-testing v0.0.0-20201019212854-469649b16807/go.mod h1:7jxmlfBCDBXRzr0eAQJ48XC1hBu1np4CS5+cHEYfwpc=
 github.com/yuin/goldmark v1.1.25/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.1.32/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=

pkg/relay/relay.go

@@ -16,6 +16,7 @@ package relay
 import (
 	"bytes"
 	"fmt"
+	"github.com/prometheus/statsd_exporter/pkg/clock"
 	"net"
 	"strings"
 	"time"
@@ -91,7 +92,7 @@ func (r *Relay) relayOutput() {
 	var buffer bytes.Buffer
 	var err error
 
-	relayInterval := time.NewTicker(1 * time.Second)
+	relayInterval := clock.NewTicker(1 * time.Second)
 	defer relayInterval.Stop()
 
 	for {

pkg/relay/relay_test.go

@@ -0,0 +1,61 @@
+package relay
+
+import (
+	"github.com/go-kit/log"
+	"github.com/prometheus/statsd_exporter/pkg/clock"
+	"github.com/stvp/go-udp-testing"
+	"testing"
+	"time"
+)
+
+func TestRelay_RelayLine(t *testing.T) {
+	type args struct {
+		lines    []string
+		expected string
+	}
+
+	tests := []struct {
+		name string
+		args args
+	}{
+		{
+			name: "single line",
+			args: args{
+				lines:    []string{"foo5:100|c|#tag1:bar,#tag2:baz"},
+				expected: "foo5:100|c|#tag1:bar,#tag2:baz\n",
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		udp.SetAddr(":1160")
+		t.Run(tt.name, func(t *testing.T) {
+
+			tickerCh := make(chan time.Time)
+			clock.ClockInstance = &clock.Clock{
+				TickerCh: tickerCh,
+			}
+			clock.ClockInstance.Instant = time.Unix(0, 0)
+
+			logger := log.NewNopLogger()
+			r, err := NewRelay(
+				logger,
+				"localhost:1160",
+				200,
+			)
+
+			if err != nil {
+				t.Errorf("Did not expect error while creating relay.")
+			}
+
+			udp.ShouldReceive(t, tt.args.expected, func() {
+				for _, line := range tt.args.lines {
+					r.RelayLine(line)
+					// Tick time forward to trigger a flush
+				}
+				clock.ClockInstance.Instant = time.Unix(20000, 0)
+				clock.ClockInstance.TickerCh <- time.Unix(20000, 0)
+			})
+		})
+	}
+}