feat: initial parser exposing walker/writer

pkg/message/parser/parser_test.go

@@ -0,0 +1,39 @@
+package parser
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func newTestParser(t *testing.T, msg string) *Parser {
+	r := f(msg)
+
+	p, err := New(r)
+	require.NoError(t, err)
+
+	return p
+}
+
+func f(filename string) io.ReadCloser {
+	f, err := os.Open(filepath.Join("testdata", filename))
+
+	if err != nil {
+		panic(err)
+	}
+
+	return f
+}
+
+func s(filename string) string {
+	b, err := ioutil.ReadAll(f(filename))
+	if err != nil {
+		panic(err)
+	}
+
+	return string(b)
+}