integration: Log the instance output

This adds logging so that you can dig deeper into crashes or issues.

integration/basic_test.go

@@ -41,6 +41,9 @@ func TestInstance0(t *testing.T) {
 	}
 	if err := m.SimpleDeployLang(code); err != nil {
 		t.Errorf("failed with: %+v", err)
+		if output, err := m.CombinedOutput(); err == nil {
+			t.Errorf("logs from instance:\n\n%s", output)
+		}
 		return
 	}
 	d := m.Dir()
@@ -98,6 +101,9 @@ func TestInstance1(t *testing.T) {
 
 			if !fail && err != nil {
 				t.Errorf("failed with: %+v", err)
+				if output, err := m.CombinedOutput(); err == nil {
+					t.Errorf("logs from instance:\n\n%s", output)
+				}
 				return
 			}
 			if fail && err == nil {
@@ -207,9 +213,15 @@ func TestCluster1(t *testing.T) {
 			if d := c.Dir(); d != "" {
 				t.Logf("test ran in:\n%s", d)
 			}
+			instances := c.Instances()
 
 			if !fail && err != nil {
 				t.Errorf("failed with: %+v", err)
+				for _, h := range hosts {
+					if output, err := instances[h].CombinedOutput(); err == nil {
+						t.Errorf("logs from instance `%s`:\n\n%s", h, output)
+					}
+				}
 				return
 			}
 			if fail && err == nil {
@@ -221,7 +233,6 @@ func TestCluster1(t *testing.T) {
 				return
 			}
 
-			instances := c.Instances()
 			for _, h := range hosts {
 				instance := instances[h]
 				d := instance.Dir()

integration/instance.go

@@ -46,6 +46,10 @@ const (
 	// converged status tracking.
 	ConvergedStatusFile = "csf.txt"
 
+	// StdoutStderrFile is the name of the file which is used for the
+	// command output.
+	StdoutStderrFile = "stdoutstderr.txt"
+
 	// longTimeout is a high bound of time we're willing to wait for events.
 	// If we exceed this timeout, then it's likely we are blocked somewhere.
 	longTimeout = 30 // seconds
@@ -206,6 +210,15 @@ func (obj *Instance) Run(seeds []*Instance) error {
 		fmt.Sprintf("MGMT_TEST_ROOT=%s", obj.testRootDirectory),
 	}
 
+	// output file for storing logs
+	file, err := os.Create(path.Join(obj.dir, StdoutStderrFile))
+	if err != nil {
+		return errwrap.Wrapf(err, "error creating log file")
+	}
+	defer file.Close()
+	obj.cmd.Stdout = file
+	obj.cmd.Stderr = file
+
 	if err := obj.cmd.Start(); err != nil {
 		return errwrap.Wrapf(err, "error starting mgmt")
 	}
@@ -368,3 +381,12 @@ func (obj *Instance) DeployLang(code string) error {
 func (obj *Instance) Dir() string {
 	return obj.dir
 }
+
+// CombinedOutput returns the logged output from the instance.
+func (obj *Instance) CombinedOutput() (string, error) {
+	contents, err := ioutil.ReadFile(path.Join(obj.dir, StdoutStderrFile))
+	if err != nil {
+		return "", err
+	}
+	return string(contents), nil
+}