test: add more tests (#1166)

* chore: reverse the order of stopping services

* chore: reverse the order of stopping services

* test: add more tests

core/retry/backoff/backoff_test.go

@@ -16,3 +16,15 @@ func TestExponential(t *testing.T) {
 	fn := Exponential(time.Second)
 	assert.EqualValues(t, time.Second, fn(1))
 }
+
+func TestLinearWithJitter(t *testing.T) {
+	const rounds = 1000000
+	var total time.Duration
+	fn := LinearWithJitter(time.Second, 0.5)
+	for i := 0; i < rounds; i++ {
+		total += fn(1)
+	}
+
+	// 0.1% tolerance
+	assert.True(t, total/time.Duration(rounds)-time.Second < time.Millisecond)
+}