Restore global logger state in tests

internal/handlers/nuget_feed_test.go

@@ -5,7 +5,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"log"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
@@ -19,6 +18,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/dependabot/proxy/internal/config"
+	"github.com/dependabot/proxy/internal/testhelpers"
 )
 
 func TestNugetFeedHandler(t *testing.T) {
@@ -113,7 +113,7 @@ func TestNugetFeedHandler(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	log.SetOutput(&buf)
+	testhelpers.CaptureStandardLog(t, &buf)
 	handler := NewNugetFeedHandler(credentials)
 
 	discoverNugetFeed(t, handler, "https://corp.dependabot.com/nuget/", http.StatusOK, mustMarshalJSON(t, rsp))
@@ -313,7 +313,7 @@ func TestExtraAuthenticatedURLsAreReportedInTheLog(t *testing.T) {
 	}`
 
 	var buf bytes.Buffer
-	log.SetOutput(&buf)
+	testhelpers.CaptureStandardLog(t, &buf)
 	handler := NewNugetFeedHandler(credentials)
 	discoverNugetFeed(t, handler, "https://nuget.example.com/index.json", http.StatusOK, jsonResponse)
 	logContents := buf.String()
@@ -555,7 +555,7 @@ func TestNugetFeedHandlerIgnoresUnusableStaticCredentials(t *testing.T) {
 
 func TestNugetFeedHandlerLogsIgnoredDuplicateResourceURL(t *testing.T) {
 	var buf bytes.Buffer
-	log.SetOutput(&buf)
+	testhelpers.CaptureStandardLog(t, &buf)
 	handler := NewNugetFeedHandler(config.Credentials{
 		testNugetFeedCredential("https://first.example.com/index.json", "first-token"),
 		testNugetFeedCredential("https://second.example.com/index.json", "second-token"),

internal/handlers/oidc_handling_test.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"log"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -16,6 +15,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/dependabot/proxy/internal/config"
+	"github.com/dependabot/proxy/internal/testhelpers"
 )
 
 type oidcHandler interface {
@@ -1557,7 +1557,7 @@ func TestOIDCURLsAreAuthenticated(t *testing.T) {
 
 			// create handler and capture log output
 			var buf bytes.Buffer
-			log.SetOutput(&buf)
+			testhelpers.CaptureStandardLog(t, &buf)
 			handler := tc.handlerFactory(tc.credentials)
 			if tc.serviceIndexURL != "" {
 				nugetHandler, ok := handler.(*NugetFeedHandler)

internal/logging/logging_test.go

@@ -3,12 +3,13 @@ package logging
 import (
 	"bytes"
 	"fmt"
-	"log"
 	"strings"
 	"testing"
 
 	"github.com/elazarl/goproxy"
 	"github.com/stretchr/testify/assert"
+
+	"github.com/dependabot/proxy/internal/testhelpers"
 )
 
 func TestRequestLogf(t *testing.T) {
@@ -60,7 +61,7 @@ func TestRequestLogf(t *testing.T) {
 	for name, tc := range testCases {
 		t.Run(name, func(t *testing.T) {
 			var buf bytes.Buffer
-			log.SetOutput(&buf)
+			testhelpers.CaptureStandardLog(t, &buf)
 
 			RequestLogf(proxyCtx, tc.format, tc.argv...)
 
@@ -119,7 +120,7 @@ func TestRequestMultilineLogf(t *testing.T) {
 	for name, tc := range testCases {
 		t.Run(name, func(t *testing.T) {
 			var buf bytes.Buffer
-			log.SetOutput(&buf)
+			testhelpers.CaptureStandardLog(t, &buf)
 
 			RequestMultilineLogf(proxyCtx, tc.format, tc.argv...)
 

internal/oidc/oidc_registry_test.go

@@ -2,9 +2,7 @@ package oidc
 
 import (
 	"bytes"
-	"log"
 	"net/http/httptest"
-	"os"
 	"strconv"
 	"strings"
 	"sync"
@@ -15,6 +13,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/dependabot/proxy/internal/config"
+	"github.com/dependabot/proxy/internal/testhelpers"
 )
 
 func setupOIDCEnv(t *testing.T) {
@@ -570,8 +569,7 @@ func TestOIDCRegistry_Register_NoDuplicateEntries(t *testing.T) {
 	cred2 := azureCredWithURL("tenant-2", "client-2", "https://registry.example.com/packages")
 
 	var logBuf bytes.Buffer
-	log.SetOutput(&logBuf)
-	defer log.SetOutput(os.Stderr)
+	testhelpers.CaptureStandardLog(t, &logBuf)
 
 	oidcCred1, key1, ok1 := r.Register(cred1, []string{"url"}, "test registry")
 	oidcCred2, key2, ok2 := r.Register(cred2, []string{"url"}, "test registry")

internal/testhelpers/logging.go

@@ -0,0 +1,49 @@
+package testhelpers
+
+import (
+	"io"
+	"log"
+	"testing"
+
+	"github.com/sirupsen/logrus"
+)
+
+// PreserveGlobalLoggerState restores the process-wide standard and Logrus
+// logger configuration after the test completes.
+func PreserveGlobalLoggerState(t testing.TB) {
+	t.Helper()
+
+	standardOutput := log.Writer()
+	standardFlags := log.Flags()
+	standardPrefix := log.Prefix()
+	logrusLogger := logrus.StandardLogger()
+	logrusOutput := logrusLogger.Out
+	logrusFormatter := logrusLogger.Formatter
+	logrusLevel := logrusLogger.GetLevel()
+	logrusReportCaller := logrusLogger.ReportCaller
+
+	t.Cleanup(func() {
+		log.SetOutput(standardOutput)
+		log.SetFlags(standardFlags)
+		log.SetPrefix(standardPrefix)
+		logrus.SetOutput(logrusOutput)
+		logrus.SetFormatter(logrusFormatter)
+		logrus.SetLevel(logrusLevel)
+		logrus.SetReportCaller(logrusReportCaller)
+	})
+}
+
+// CaptureStandardLog redirects the standard logger for the duration of a test.
+func CaptureStandardLog(t testing.TB, output io.Writer) {
+	t.Helper()
+	PreserveGlobalLoggerState(t)
+	log.SetOutput(output)
+}
+
+// CaptureGlobalLogs redirects the standard and Logrus loggers for a test.
+func CaptureGlobalLogs(t testing.TB, output io.Writer) {
+	t.Helper()
+	PreserveGlobalLoggerState(t)
+	log.SetOutput(output)
+	logrus.SetOutput(output)
+}

internal/testhelpers/logging_test.go

@@ -0,0 +1,40 @@
+package testhelpers
+
+import (
+	"io"
+	"log"
+	"testing"
+
+	"github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPreserveGlobalLoggerState(t *testing.T) {
+	standardOutput := log.Writer()
+	standardFlags := log.Flags()
+	standardPrefix := log.Prefix()
+	logrusLogger := logrus.StandardLogger()
+	logrusOutput := logrusLogger.Out
+	logrusFormatter := logrusLogger.Formatter
+	logrusLevel := logrusLogger.GetLevel()
+	logrusReportCaller := logrusLogger.ReportCaller
+
+	t.Run("mutate logger state", func(t *testing.T) {
+		PreserveGlobalLoggerState(t)
+		log.SetOutput(io.Discard)
+		log.SetFlags(0)
+		log.SetPrefix("test-prefix")
+		logrus.SetOutput(io.Discard)
+		logrus.SetFormatter(&logrus.JSONFormatter{})
+		logrus.SetLevel(logrus.DebugLevel)
+		logrus.SetReportCaller(!logrusReportCaller)
+	})
+
+	assert.Equal(t, standardOutput, log.Writer())
+	assert.Equal(t, standardFlags, log.Flags())
+	assert.Equal(t, standardPrefix, log.Prefix())
+	assert.Equal(t, logrusOutput, logrusLogger.Out)
+	assert.Equal(t, logrusFormatter, logrusLogger.Formatter)
+	assert.Equal(t, logrusLevel, logrusLogger.GetLevel())
+	assert.Equal(t, logrusReportCaller, logrusLogger.ReportCaller)
+}

logging_test.go

@@ -20,6 +20,8 @@ import (
 	"github.com/sirupsen/logrus"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/dependabot/proxy/internal/testhelpers"
 )
 
 var timestamp = regexp.MustCompile(`\d{4}/\d{2}/{2} \d{2}:\d{2}:\d{2} `)
@@ -155,7 +157,7 @@ func TestRequestLogger(t *testing.T) {
 			}
 
 			var buf bytes.Buffer
-			log.SetOutput(&buf)
+			testhelpers.CaptureStandardLog(t, &buf)
 			l := NewRequestLogger()
 			if tc.setup != nil {
 				tc.setup(t, l)
@@ -191,6 +193,7 @@ func TestRequestLogger(t *testing.T) {
 }
 
 func TestSetupLogging(t *testing.T) {
+	testhelpers.PreserveGlobalLoggerState(t)
 	temp := t.TempDir()
 	logFile := path.Join(temp, "test.log")
 	logfilePath = &logFile

proxy_test.go

@@ -10,7 +10,6 @@ import (
 	"crypto/x509/pkix"
 	"encoding/pem"
 	"io"
-	"log"
 	"math/big"
 	"net"
 	"net/http"
@@ -20,11 +19,11 @@ import (
 	"testing"
 	"time"
 
-	"github.com/sirupsen/logrus"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"github.com/dependabot/proxy/internal/config"
+	"github.com/dependabot/proxy/internal/testhelpers"
 )
 
 var (
@@ -306,12 +305,7 @@ func TestProxyHTTPSConditionalNotModifiedPreservesCachedResponse(t *testing.T) {
 // identical request can still succeed.
 func TestProxyUpstreamCloseIsNotCachedAsBodylessResponse(t *testing.T) {
 	var logOutput bytes.Buffer
-	originalLogOutput := log.Writer()
-	originalLogrusOutput := logrus.StandardLogger().Out
-	log.SetOutput(&logOutput)
-	logrus.SetOutput(&logOutput)
-	defer log.SetOutput(originalLogOutput)
-	defer logrus.SetOutput(originalLogrusOutput)
+	testhelpers.CaptureGlobalLogs(t, &logOutput)
 
 	var upstreamRequests atomic.Int32
 	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {