functional: add new tests for the replace option

TestUnit{Submit,Load,Start}Replace() tests whether a command "fleetctl
{submit,load,start} --replace hello.service" works respectively.
As most of the test sequences are identical, the common part is split
into replaceUnitCommon().

functional/unit_action_test.go

@@ -17,12 +17,18 @@ package functional
 import (
 	"fmt"
 	"io/ioutil"
+	"os"
 	"strings"
 	"testing"
 
 	"github.com/coreos/fleet/functional/platform"
 )
 
+const (
+	tmpHelloService = "/tmp/hello.service"
+	fxtHelloService = "fixtures/units/hello.service"
+)
+
 // TestUnitRunnable is the simplest test possible, deplying a single-node
 // cluster and ensuring a unit can enter an 'active' state
 func TestUnitRunnable(t *testing.T) {
@@ -169,6 +175,30 @@ func TestUnitRestart(t *testing.T) {
 
 }
 
+// TestUnitSubmitReplace() tests whether a command "fleetctl submit --replace
+// hello.service" works or not.
+func TestUnitSubmitReplace(t *testing.T) {
+	if err := replaceUnitCommon("submit"); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// TestUnitLoadReplace() tests whether a command "fleetctl load --replace
+// hello.service" works or not.
+func TestUnitLoadReplace(t *testing.T) {
+	if err := replaceUnitCommon("load"); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// TestUnitStartReplace() tests whether a command "fleetctl start --replace
+// hello.service" works or not.
+func TestUnitStartReplace(t *testing.T) {
+	if err := replaceUnitCommon("start"); err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestUnitSSHActions(t *testing.T) {
 	cluster, err := platform.NewNspawnCluster("smoke")
 	if err != nil {
@@ -227,6 +257,74 @@ func TestUnitSSHActions(t *testing.T) {
 	}
 }
 
+// replaceUnitCommon() tests whether a command "fleetctl {submit,load,start}
+// --replace hello.service" works or not.
+func replaceUnitCommon(cmd string) error {
+	// check if cmd is one of the supported commands.
+	listCmds := []string{"submit", "load", "start"}
+	found := false
+	for _, ccmd := range listCmds {
+		if ccmd == cmd {
+			found = true
+		}
+	}
+	if !found {
+		return fmt.Errorf("invalid command %s", cmd)
+	}
+
+	cluster, err := platform.NewNspawnCluster("smoke")
+	if err != nil {
+		return fmt.Errorf("%v", err)
+	}
+	defer cluster.Destroy()
+
+	m, err := cluster.CreateMember()
+	if err != nil {
+		return fmt.Errorf("%v", err)
+	}
+	_, err = cluster.WaitForNMachines(m, 1)
+	if err != nil {
+		return fmt.Errorf("%v", err)
+	}
+
+	// run a command for a unit and assert it shows up
+	if _, _, err := cluster.Fleetctl(m, cmd, fxtHelloService); err != nil {
+		return fmt.Errorf("Unable to %s fleet unit: %v", cmd, err)
+	}
+	stdout, _, err := cluster.Fleetctl(m, "list-units", "--no-legend")
+	if err != nil {
+		return fmt.Errorf("Failed to run list-units: %v", err)
+	}
+	units := strings.Split(strings.TrimSpace(stdout), "\n")
+	if len(units) != 1 {
+		return fmt.Errorf("Did not find 1 unit in cluster: \n%s", stdout)
+	}
+
+	// replace the unit and assert it shows up
+	err = genNewFleetService(tmpHelloService, fxtHelloService, "sleep 2", "sleep 1")
+	if err != nil {
+		return fmt.Errorf("Failed to generate a temp fleet service: %v", err)
+	}
+	if _, _, err := cluster.Fleetctl(m, cmd, "--replace", tmpHelloService); err != nil {
+		return fmt.Errorf("Unable to replace fleet unit: %v", err)
+	}
+	stdout, _, err = cluster.Fleetctl(m, "list-units", "--no-legend")
+	if err != nil {
+		return fmt.Errorf("Failed to run list-units: %v", err)
+	}
+	units = strings.Split(strings.TrimSpace(stdout), "\n")
+	if len(units) != 1 {
+		return fmt.Errorf("Did not find 1 unit in cluster: \n%s", stdout)
+	}
+	os.Remove(tmpHelloService)
+
+	if err := destroyUnitRetrying(cluster, m, fxtHelloService); err != nil {
+		return fmt.Errorf("Cannot destroy unit %v", fxtHelloService)
+	}
+
+	return nil
+}
+
 // genNewFleetService() is a helper for generating a temporary fleet service
 // that reads from oldFile, replaces oldVal with newVal, and stores the result
 // to newFile.