Add unit tests.

plugins/inputs/windows_event_log/service_monitor.go

@@ -7,7 +7,7 @@
 package windows_event_log
 
 import (
-	"fmt"
+	"errors"
 	"log"
 	"time"
 
@@ -21,6 +21,14 @@ const (
 	serviceName = "eventlog"
 )
 
+var (
+	errServiceNotRunning = errors.New("service is not running")
+)
+
+type statusChecker interface {
+	Query() (svc.Status, error)
+}
+
 type serviceMonitor struct {
 	listeners []chan struct{}
 	done      chan struct{}
@@ -82,13 +90,13 @@ func (m *serviceMonitor) notify() {
 	}
 }
 
-func getPID(service *mgr.Service) (uint32, error) {
+func getPID(service statusChecker) (uint32, error) {
 	status, err := service.Query()
 	if err != nil {
 		return 0, err
 	}
 	if status.State == svc.Running {
 		return status.ProcessId, nil
 	}
-	return 0, fmt.Errorf("service is not running")
+	return 0, errServiceNotRunning
 }

plugins/inputs/windows_event_log/service_monitor_test.go

@@ -0,0 +1,62 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build windows
+// +build windows
+
+package windows_event_log
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"golang.org/x/sys/windows/svc"
+)
+
+type mockStatusCheck struct {
+	status svc.Status
+	err    error
+}
+
+func (m *mockStatusCheck) Query() (svc.Status, error) {
+	return m.status, m.err
+}
+
+func TestGetPID(t *testing.T) {
+	testErr := errors.New("test error")
+	testCases := map[string]struct {
+		status  svc.Status
+		err     error
+		wantPID uint32
+		wantErr error
+	}{
+		"WithQueryError": {
+			err:     testErr,
+			wantPID: 0,
+			wantErr: testErr,
+		},
+		"WithStoppedService": {
+			status: svc.Status{
+				State:     svc.Stopped,
+				ProcessId: 0,
+			},
+			wantPID: 0,
+			wantErr: errServiceNotRunning,
+		},
+		"WithRunningService": {
+			status: svc.Status{
+				State:     svc.Running,
+				ProcessId: 123,
+			},
+			wantPID: 123,
+		},
+	}
+	for name, testCase := range testCases {
+		t.Run(name, func(t *testing.T) {
+			gotPID, gotErr := getPID(&mockStatusCheck{status: testCase.status, err: testCase.err})
+			assert.Equal(t, testCase.wantPID, gotPID)
+			assert.Equal(t, testCase.wantErr, gotErr)
+		})
+	}
+}

plugins/inputs/windows_event_log/wineventlog/wineventlog.go

@@ -89,15 +89,7 @@ func NewEventLog(name string, levels []string, logGroupName, logStreamName, rend
 func (w *windowsEventLog) Init() error {
 	go w.runSaveState()
 	w.eventOffset = w.loadState()
-	// Subscribe for events.
-	// This will fail if the eventlog name has not been registered.
-	// However returning an error would mean the plugin won't monitor other eventlogs.
-	err := w.Open()
-	if werr, ok := err.(*wevtAPIError); ok && werr.api == apiEvtSubscribe {
-		log.Printf("W! [wineventlog] %v", err)
-		return nil
-	}
-	return err
+	return w.Open()
 }
 
 func (w *windowsEventLog) SetOutput(fn func(logs.LogEvent)) {
@@ -177,7 +169,18 @@ func (w *windowsEventLog) run() {
 	}
 }
 
+// Open subscription for events. Instead of failing the subscription if the eventlog name has not been registered,
+// log the error.
 func (w *windowsEventLog) Open() error {
+	err := w.open()
+	if werr, ok := err.(*wevtAPIError); ok && werr.api == apiEvtSubscribe {
+		log.Printf("W! [wineventlog] %v", err)
+		return nil
+	}
+	return err
+}
+
+func (w *windowsEventLog) open() error {
 	bookmark, err := CreateBookmark(w.name, w.eventOffset)
 	if err != nil {
 		return err
@@ -218,7 +221,7 @@ func (w *windowsEventLog) resubscribe() error {
 		}
 	}
 	w.eventHandle = EvtHandle(0)
-	return w.Open()
+	return w.open()
 }
 
 func (w *windowsEventLog) LogGroupName() string {