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// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
package tap
import (
// Producer produces TAP output.
// This producer always includes test numbers.
type Producer struct {
output io.Writer
directive Directive
testNumber int
// NewProducer creates a new Producer that writes to the given Writer.
func NewProducer(w io.Writer) *Producer {
p := &Producer{
output: w,
directive: None,
// Output the TAP version line.
p.writeln("TAP version 13")
return p
// Plan outputs the TAP plan line: 1..count. If count <= 0, nothing is printed
func (p *Producer) Plan(count int) {
if count > 0 {
p.writeln("1..%d", count)
// Ok outputs a test line containing the given description and starting with either "ok"
// if test is true or "not ok" if false. If this producer was created using
// Todo or Skip, then the corresponding directive is also printed, and the description is
// used as the explanation of that directive.
func (p *Producer) Ok(test bool, description string) {
ok := "ok"
if !test {
ok = "not ok"
switch p.directive {
case None:
p.writeln("%s %d %s", ok, p.testNumber, description)
case Todo:
p.writeln("%s %d # TODO %s", ok, p.testNumber, description)
case Skip:
p.writeln("%s %d # SKIP %s", ok, p.testNumber, description)
p.directive = None
// YAML produces a YAML block from the given input. This will indent the input data. The
// caller should not do this themselves.
func (p *Producer) YAML(input []byte) {
// Chomp empty lines from the end of the document.
content := strings.TrimSuffix(string(input), "\n")
// Todo returns a new Producer that prints TODO directives.
func (p *Producer) Todo() *Producer {
p.directive = Todo
return p
// Skip returns a new Producer that prints SKIP directives.
func (p *Producer) Skip() *Producer {
p.directive = Skip
return p
func (p *Producer) writeln(format string, args ...interface{}) {
fmt.Fprintln(p.writer(), fmt.Sprintf(format, args...))
// writer initializes the Writer to use for this Producer, in case the Producer was
// initialized with nil output.
func (p *Producer) writer() io.Writer {
if p.output == nil {
p.output = os.Stdout
return p.output
// Indent indents every line of the input text with a single space.
func (p *Producer) indent(input string) string {
return string(p.indentBytes([]byte(input)))
// IndentBytes indents every line of the input text with a single space.
func (p *Producer) indentBytes(input []byte) []byte {
var output []byte
startOfLine := true
for _, c := range input {
if startOfLine && c != '\n' {
output = append(output, ' ')
output = append(output, c)
startOfLine = c == '\n'
return output