Test Helpers and Golden Files

The test below calls a helper three times, and one of the three calls fails. The expected value in the last call is wrong on purpose, so that a failure report appears.

// file: order.go
package orders

type Item struct {
	SKU      string
	Quantity int
	Cents    int64
}

type Order struct {
	ID    int64
	Items []Item
}

func (o Order) Total() int64 {
	var total int64
	for _, item := range o.Items {
		total += int64(item.Quantity) * item.Cents
	}
	return total
}
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// file: order_test.go
package orders

import "testing"

func checkTotal(t *testing.T, o Order, want int64) {
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