Add test for verifying proper shutdown

Signed-off-by: Paschalis Tsilias <paschalis.tsilias@grafana.com>

internal/examples/supervisor/supervisor/supervisor_test.go

@@ -4,7 +4,8 @@ import (
 	"fmt"
 	"os"
 	"testing"
-
+	"time"
+
 	"github.com/stretchr/testify/assert"
 
 	"github.com/open-telemetry/opamp-go/internal"
@@ -62,3 +63,33 @@ agent:
 
 	supervisor.Shutdown()
 }
+
+func TestShutdownRaceCondition(t *testing.T) {
+	tmpDir := changeCurrentDir(t)
+	os.WriteFile("supervisor.yaml", []byte(fmt.Sprintf(`
+server:
+  endpoint: ws://127.0.0.1:4320/v1/opamp
+agent:
+  executable: %s/dummy_agent.sh`, tmpDir)), 0644)
+
+	os.WriteFile("dummy_agent.sh", []byte("#!/bin/sh\nsleep 9999\n"), 0755)
+
+	startOpampServer(t)
+
+	// There's no great way to ensure Shutdown gets called before Start.
+	// The DelayLogger ensures some delay before the goroutine gets started.
+	var supervisor *Supervisor
+	var err error
+	supervisor, err = NewSupervisor(&internal.DelayLogger{})
+	supervisor.Shutdown()
+	supervisor.hasNewConfig <- struct{}{}
+
+	assert.NoError(t, err)
+
+	// The Shutdown method has been called before the runAgentProcess goroutine
+	// gets started and has a chance to load a new process. Make sure no PID
+	// has been launched.
+	assert.Never(t, func() bool {
+		return supervisor.commander.Pid() != 0
+	}, 2*time.Second, 10*time.Millisecond)
+}

internal/noplogger.go

@@ -2,6 +2,7 @@ package internal
 
 import (
 	"context"
+	"time"
 
 	"github.com/open-telemetry/opamp-go/client/types"
 )
@@ -12,3 +13,12 @@ type NopLogger struct{}
 
 func (l *NopLogger) Debugf(ctx context.Context, format string, v ...interface{}) {}
 func (l *NopLogger) Errorf(ctx context.Context, format string, v ...interface{}) {}
+
+type DelayLogger struct{}
+
+func (l *DelayLogger) Debugf(ctx context.Context, format string, v ...interface{}) {
+	time.Sleep(10 * time.Millisecond)
+}
+func (l *DelayLogger) Errorf(ctx context.Context, format string, v ...interface{}) {
+	time.Sleep(10 * time.Millisecond)
+}