jobs: fix TestJitterCalculation failed

This test will sometimes fail due to a randomly picking a value that
rounds to 1/2. The frequency of this is a bit higher than one would
expect because the rounding behavior depends on the width of the
duration, not the width of a float64. The test was adjusted to retry
if the jittered value equals the input.

Release note: none
Fixes: #128381
Fixes: #157113

Author: jeffswenson

pkg/jobs/registry_test.go

@@ -9,6 +9,7 @@ import (
 	"context"
 	gosql "database/sql"
 	"fmt"
+	"math/rand"
 	"strconv"
 	"strings"
 	"sync/atomic"
@@ -710,13 +711,17 @@ func TestJitterCalculation(t *testing.T) {
 		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
-			interval := jitter(test.input)
+			interval := test.input
+			testutils.SucceedsSoon(t, func() error {
+				interval = jitter(test.input)
+				if interval == test.input {
+					return errors.New("jitter returned same value as input")
+				}
+				return nil
+			})
 			rangeMin, rangeMax := outputRange(test.input)
 			require.GreaterOrEqual(t, rangeMax, interval)
 			require.LessOrEqual(t, rangeMin, interval)
-			if test.input != 0 {
-				require.NotEqual(t, test.input, interval)
-			}
 		})
 	}
 }