test: make PanicCheck an implicit Assert gadget

When running "Assert" on a packer command, we run a series of checkers
on the command's output/error code, which provoke test failures if they
fail.

Panic checking used to be part of Run, but in the end this would make
more sense to have that as a regular checker if asserting the results of
a packer command, so that's the approach we adopt with this commit.

test/commands_test.go

@@ -53,13 +53,9 @@ func (pc *packerCommand) AddEnv(key, val string) *packerCommand {
 //
 // Note: "Run" will only execute the command once, and return the streams and
 // error from the only execution for every subsequent call
-func (pc *packerCommand) Run(t *testing.T) (string, string, error) {
+func (pc *packerCommand) Run() (string, string, error) {
 	pc.once.Do(pc.doRun)
 
-	if strings.Contains(pc.stdout.String(), "PACKER CRASH") || strings.Contains(pc.stderr.String(), "PACKER CRASH") {
-		t.Fatalf("Packer has crashed while running the following command: packer %#v", pc.args)
-	}
-
 	return pc.stdout.String(), pc.stderr.String(), pc.err
 }
 
@@ -75,7 +71,9 @@ func (pc *packerCommand) doRun() {
 }
 
 func (pc *packerCommand) Assert(t *testing.T, checks ...Checker) {
-	stdout, stderr, err := pc.Run(t)
+	stdout, stderr, err := pc.Run()
+
+	checks = append(checks, PanicCheck{})
 
 	for _, check := range checks {
 		checkErr := check.Check(stdout, stderr, err)

test/gadgets_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"reflect"
 	"regexp"
+	"strings"
 	"testing"
 )
 
@@ -117,3 +118,12 @@ func (d Dump) Check(stdout, stderr string, err error) error {
 	d.t.Logf("stderr: %s", stderr)
 	return nil
 }
+
+type PanicCheck struct{}
+
+func (_ PanicCheck) Check(stdout, stderr string, _ error) error {
+	if strings.Contains(stdout, "= PACKER CRASH =") || strings.Contains(stderr, "= PACKER CRASH =") {
+		return fmt.Errorf("packer has crashed: this is never normal and should be investigated")
+	}
+	return nil
+}

test/plugin_test.go

@@ -161,7 +161,7 @@ func (ts *PackerTestSuite) MakePluginDir(pluginVersions ...string) (pluginTempDi
 		path, _ := LoadPluginVersion(pluginVersion)
 		cmd := ts.PackerCommand().SetArgs("plugins", "install", "--path", path, "github.com/hashicorp/tester").AddEnv("PACKER_PLUGIN_PATH", pluginTempDir)
 		cmd.Assert(t, MustSucceed{})
-		out, stderr, cmdErr := cmd.Run(t)
+		out, stderr, cmdErr := cmd.Run()
 		if cmdErr != nil {
 			err = fmt.Errorf("failed to install tester plugin version %q: %s\nCommand stdout: %s\nCommand stderr: %s", pluginVersion, err, out, stderr)
 			return