Testing file for the implementation of fmt.Fscanf

ppm_test.go

package ppm

import "fmt"
import "io"
import "testing"

// io.Reader for TestFscanf. We use our own reader to be sure that pushing back
// is not supported.
type fscanfTestReader struct {
	content []byte
	count   int
}

func (this *fscanfTestReader) Read(buf []byte) (n int, err error) {
	n = len(buf)
	m := len(this.content)

	if n > m {
		err = io.EOF
		n = m
	}

	copy(buf, this.content)
	this.content = this.content[n:]
	this.count += n

	return
}

// The code in ppm.go assumes that if the last formatting verb passed to Fscanf
// is %c it is guaranteed that Fscanf does not consume more input than needed.
// This assumption is needed to make parsing the header of a PPM-file with the
// functions provided by fmt possible while keeping the ability to be certain
// that we do not consume more of the input than we need.
func TestFscanf(t *testing.T) {
	var d int
	var c byte
	r := fscanfTestReader{([]byte)("1234xy"), 0}

	items, err := fmt.Fscanf(&r, "%d%c", &d, &c)

	if r.count != 5 || items != 2 {
		t.Error("Fscanf behavior does not conform")
	}

	if err != nil {
		t.Error(err.Error())
	}
}