[#293] pkg: Implement and use generators of the messages

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/test/generate.go

@@ -0,0 +1,51 @@
+package refstest
+
+import (
+	"crypto/sha256"
+	"math/rand"
+
+	"github.com/nspcc-dev/neofs-api-go/pkg"
+)
+
+// Checksum returns random pkg.Checksum.
+func Checksum() *pkg.Checksum {
+	var cs [sha256.Size]byte
+
+	rand.Read(cs[:])
+
+	x := pkg.NewChecksum()
+
+	x.SetSHA256(cs)
+
+	return x
+}
+
+// Signature returns random pkg.Signature.
+func Signature() *pkg.Signature {
+	x := pkg.NewSignature()
+
+	x.SetKey([]byte("key"))
+	x.SetSign([]byte("sign"))
+
+	return x
+}
+
+// Version returns random pkg.Version.
+func Version() *pkg.Version {
+	x := pkg.NewVersion()
+
+	x.SetMajor(2)
+	x.SetMinor(1)
+
+	return x
+}
+
+// XHeader returns random pkg.XHeader.
+func XHeader() *pkg.XHeader {
+	x := pkg.NewXHeader()
+
+	x.SetKey("key")
+	x.SetValue("value")
+
+	return x
+}