Fixing the limit test and improving an example

Just now realizing that the limit strategy has had an off-by-one error
for 5+ years now...

Not sure what I was thinking here:
678601c

example_test.go

@@ -69,6 +69,8 @@ func Example_httpGetWithStrategies() {
 
 func Example_withBackoffJitter() {
 	action := func(attempt uint) error {
+		fmt.Println("attempt", attempt)
+
 		return errors.New("something happened")
 	}
 
@@ -83,4 +85,11 @@ func Example_withBackoffJitter() {
 			jitter.Deviation(random, 0.5),
 		),
 	)
+
+	// Output:
+	// attempt 1
+	// attempt 2
+	// attempt 3
+	// attempt 4
+	// attempt 5
 }

strategy/strategy_test.go

@@ -10,23 +10,25 @@ import (
 const timeMarginOfError = time.Millisecond
 
 func TestLimit(t *testing.T) {
+	// Strategy attempts are 0-based.
+	// Treat this functionally as n+1.
 	const attemptLimit = 3
 
 	strategy := Limit(attemptLimit)
 
-	if !strategy(1) {
+	if !strategy(0) {
 		t.Error("strategy expected to return true")
 	}
 
-	if !strategy(2) {
+	if !strategy(1) {
 		t.Error("strategy expected to return true")
 	}
 
-	if !strategy(3) {
+	if !strategy(2) {
 		t.Error("strategy expected to return true")
 	}
 
-	if strategy(4) {
+	if strategy(3) {
 		t.Error("strategy expected to return false")
 	}
 }