Fix TestBackoffRetry in otlp/internal/retry package (#2562)

* Fix TestBackoffRetry in otlp retry pkg

The delay of the retry is within two times a randomization factor (the
back-off time is delay * random number within [1 - factor, 1 + factor].
This means the waitFunc in TestBackoffRetry needs to check the delay is
within an appropriate delta, not equal to configure initial delay.

* Fix delta value

* Fix delta

Co-authored-by: Aaron Clawson <Aaron.Clawson@gmail.com>

exporters/otlp/internal/retry/retry_test.go

@@ -17,9 +17,11 @@ package retry
 import (
 	"context"
 	"errors"
+	"math"
 	"testing"
 	"time"
 
+	"github.com/cenkalti/backoff/v4"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -131,15 +133,16 @@ func TestBackoffRetry(t *testing.T) {
 	origWait := waitFunc
 	var done bool
 	waitFunc = func(_ context.Context, d time.Duration) error {
-		assert.Equal(t, delay, d, "retry not backoffed")
+		delta := math.Ceil(float64(delay)*backoff.DefaultRandomizationFactor) - float64(delay)
+		assert.InDelta(t, delay, d, delta, "retry not backoffed")
 		// Try twice to ensure call is attempted again after delay.
 		if done {
 			return assert.AnError
 		}
 		done = true
 		return nil
 	}
-	defer func() { waitFunc = origWait }()
+	t.Cleanup(func() { waitFunc = origWait })
 
 	ctx := context.Background()
 	assert.ErrorIs(t, reqFunc(ctx, func(context.Context) error {