Use sebdah/goldie for Golden File Testing

[tri-adam]

Use sebdah/goldie for golden file testing, to replace custom code that does the same thing:

sif/pkg/integrity/main_test.go

Lines 87 to 124 in da34172

	// goldenPath returns the path of the golden file corresponding to name.
	func goldenPath(name string) string {
	// Replace test name separator with OS-specific path separator.
	name = path.Join(strings.Split(name, "/")...)
	return path.Join("testdata", name) + ".golden"
	}
	// updateGolden writes b to a golden file associated with name.
	func updateGolden(name string, b []byte) error {
	p := goldenPath(name)
	if err := os.MkdirAll(path.Dir(p), 0755); err != nil {
	return err
	}
	return ioutil.WriteFile(p, b, 0644) // nolint:gosec
	}
	// verifyGolden compares b to the contents golden file associated with name.
	func verifyGolden(name string, r io.Reader) error {
	b, err := ioutil.ReadAll(r)
	if err != nil {
	return err
	}
	if *update {
	if err := updateGolden(name, b); err != nil {
	return err
	}
	}
	g, err := ioutil.ReadFile(goldenPath(name))
	if err != nil {
	return err
	}
	if !bytes.Equal(b, g) {
	return errors.New("output does not match golden file")
	}
	return nil
	}