Do test that a helm plugin can return non-zero exit code other than 1

Signed-off-by: Yusuke Kuoka <ykuoka@gmail.com>

cmd/helm/helm_test.go

@@ -20,6 +20,8 @@ import (
 	"bytes"
 	"io/ioutil"
 	"os"
+	"os/exec"
+	"runtime"
 	"strings"
 	"testing"
 
@@ -151,3 +153,59 @@ func testChdir(t *testing.T, dir string) func() {
 	}
 	return func() { os.Chdir(old) }
 }
+
+func TestPluginExitCode(t *testing.T) {
+	if os.Getenv("RUN_MAIN_FOR_TESTING") == "1" {
+		os.Args = []string{"helm", "exitwith", "2"}
+
+		// We DO call helm's main() here. So this looks like a normal `helm` process.
+		main()
+
+		// As main calls os.Exit, we never reach this line.
+		// But the test called this block of code catches and verifies the exit code.
+		return
+	}
+
+	// Currently, plugins assume a Linux subsystem. Skip the execution
+	// tests until this is fixed
+	if runtime.GOOS != "windows" {
+		// Do a second run of this specific test(TestPluginExitCode) with RUN_MAIN_FOR_TESTING=1 set,
+		// So that the second run is able to run main() and this first run can verify the exit status returned by that.
+		//
+		// This technique originates from https://talks.golang.org/2014/testing.slide#23.
+		cmd := exec.Command(os.Args[0], "-test.run=TestPluginExitCode")
+		cmd.Env = append(
+			os.Environ(),
+			"RUN_MAIN_FOR_TESTING=1",
+			// See pkg/cli/environment.go for which envvars can be used for configuring these passes
+			// and also see plugin_test.go for how a plugin env can be set up.
+			// We just does the same setup as plugin_test.go via envvars
+			"HELM_PLUGINS=testdata/helmhome/helm/plugins",
+			"HELM_REPOSITORY_CONFIG=testdata/helmhome/helm/repositories.yaml",
+			"HELM_REPOSITORY_CACHE=testdata/helmhome/helm/repository",
+		)
+		stdout := &bytes.Buffer{}
+		stderr := &bytes.Buffer{}
+		cmd.Stdout = stdout
+		cmd.Stderr = stderr
+		err := cmd.Run()
+		exiterr, ok := err.(*exec.ExitError)
+
+		if !ok {
+			t.Fatalf("Unexpected error returned by os.Exit: %T", err)
+		}
+
+		if stdout.String() != "" {
+			t.Errorf("Expected no write to stdout: Got %q", stdout.String())
+		}
+
+		expectedStderr := "Error: plugin \"exitwith\" exited with error\n"
+		if stderr.String() != expectedStderr {
+			t.Errorf("Expected %q written to stderr: Got %q", expectedStderr, stderr.String())
+		}
+
+		if exiterr.ExitCode() != 2 {
+			t.Errorf("Expected exit code 2: Got %d", exiterr.ExitCode())
+		}
+	}
+}