Improve unit test of flowexporter package

Fix one of the unit test TestFlowExporter_sendFlowRecords, and
adds a testcase to TestFlowExporter_initFlowExporter.

For antrea-io#4142

Signed-off-by: heanlan <hanlan@vmware.com>

pkg/agent/flowexporter/exporter/exporter_test.go

@@ -268,21 +268,42 @@ func TestFlowExporter_initFlowExporter(t *testing.T) {
 	if err != nil {
 		t.Fatalf("error when resolving UDP address: %v", err)
 	}
-	conn, err := net.ListenUDP("udp", udpAddr)
+	conn1, err := net.ListenUDP("udp", udpAddr)
 	if err != nil {
 		t.Fatalf("error when creating a local server: %v", err)
 	}
-	defer conn.Close()
-	exp := &FlowExporter{
-		process: nil,
-		exporterInput: exporter.ExporterInput{
-			CollectorProtocol: conn.LocalAddr().Network(),
-			CollectorAddress:  conn.LocalAddr().String(),
-		},
+	defer conn1.Close()
+	tcpAddr, err := net.ResolveTCPAddr("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("error when resolving TCP address: %v", err)
+	}
+	conn2, err := net.ListenTCP("tcp", tcpAddr)
+	if err != nil {
+		t.Fatalf("error when creating a local server: %v", err)
+	}
+	defer conn2.Close()
+
+	for _, tc := range []struct {
+		protocol               string
+		address                string
+		expectedTempRefTimeout uint32
+	}{
+		{conn1.LocalAddr().Network(), conn1.LocalAddr().String(), uint32(1800)},
+		{conn2.Addr().Network(), conn2.Addr().String(), uint32(0)},
+	} {
+		exp := &FlowExporter{
+			process: nil,
+			exporterInput: exporter.ExporterInput{
+				CollectorProtocol: tc.protocol,
+				CollectorAddress:  tc.address,
+			},
+		}
+		err = exp.initFlowExporter()
+		assert.NoError(t, err)
+		assert.Equal(t, tc.expectedTempRefTimeout, exp.exporterInput.TempRefTimeout)
+		checkTotalReconnectionsMetric(t)
+		metrics.ReconnectionsToFlowCollector.Dec()
 	}
-	err = exp.initFlowExporter()
-	assert.NoError(t, err)
-	checkTotalReconnectionsMetric(t)
 }
 
 func checkTotalReconnectionsMetric(t *testing.T) {
@@ -422,7 +443,8 @@ func testSendFlowRecords(t *testing.T, v4Enabled bool, v6Enabled bool) {
 		elementsListv6: elemListv6,
 		templateIDv4:   testTemplateIDv4,
 		templateIDv6:   testTemplateIDv6,
-		v4Enabled:      true}
+		v4Enabled:      v4Enabled,
+		v6Enabled:      v6Enabled}
 
 	if v4Enabled {
 		runSendFlowRecordTests(t, flowExp, false)