Fix panic in acceptance tests (#3592)

* Fix panic in acceptance tests

This commit attempts to address a panic that occurs in acceptance
tests if a server in the cluster fails to start.

Signed-off-by: George Robinson <george.robinson@grafana.com>

* Remove started and check am.cmd.Process != nil

Signed-off-by: George Robinson <george.robinson@grafana.com>

---------

Signed-off-by: George Robinson <george.robinson@grafana.com>

test/with_api_v2/acceptance.go

@@ -169,17 +169,15 @@ func (t *AcceptanceTest) Run() {
 
 	for _, am := range t.amc.ams {
 		am.errc = errc
-		defer func(am *Alertmanager) {
-			am.Terminate()
-			am.cleanup()
-			t.Logf("stdout:\n%v", am.cmd.Stdout)
-			t.Logf("stderr:\n%v", am.cmd.Stderr)
-		}(am)
+		t.T.Cleanup(am.Terminate)
+		t.T.Cleanup(am.cleanup)
 	}
 
 	err := t.amc.Start()
 	if err != nil {
-		t.T.Fatal(err)
+		t.T.Log(err)
+		t.T.Fail()
+		return
 	}
 
 	// Set the reference time right before running the test actions to avoid
@@ -251,10 +249,10 @@ type Alertmanager struct {
 	apiAddr     string
 	clusterAddr string
 	clientV2    *apiclient.AlertmanagerAPI
-	cmd         *exec.Cmd
 	confFile    *os.File
 	dir         string
 
+	cmd  *exec.Cmd
 	errc chan<- error
 }
 
@@ -386,8 +384,12 @@ func (amc *AlertmanagerCluster) Terminate() {
 // data.
 func (am *Alertmanager) Terminate() {
 	am.t.Helper()
-	if err := syscall.Kill(am.cmd.Process.Pid, syscall.SIGTERM); err != nil {
-		am.t.Logf("Error sending SIGTERM to Alertmanager process: %v", err)
+	if am.cmd.Process != nil {
+		if err := syscall.Kill(am.cmd.Process.Pid, syscall.SIGTERM); err != nil {
+			am.t.Logf("Error sending SIGTERM to Alertmanager process: %v", err)
+		}
+		am.t.Logf("stdout:\n%v", am.cmd.Stdout)
+		am.t.Logf("stderr:\n%v", am.cmd.Stderr)
 	}
 }
 
@@ -401,8 +403,10 @@ func (amc *AlertmanagerCluster) Reload() {
 // Reload sends the reloading signal to the Alertmanager process.
 func (am *Alertmanager) Reload() {
 	am.t.Helper()
-	if err := syscall.Kill(am.cmd.Process.Pid, syscall.SIGHUP); err != nil {
-		am.t.Fatalf("Error sending SIGHUP to Alertmanager process: %v", err)
+	if am.cmd.Process != nil {
+		if err := syscall.Kill(am.cmd.Process.Pid, syscall.SIGHUP); err != nil {
+			am.t.Fatalf("Error sending SIGHUP to Alertmanager process: %v", err)
+		}
 	}
 }