light: model-based tests (#5461)

This is the first iteration of model-based testing in Go Tendermint. The test runner is using the static JSON fixtures located under the ./json directory. In the future, the Rust tensgen binary will be used to generate those (given the static intermediate scenarios and the test seed, which will be published along with each testgen release).

Closes: #5322

libs/bytes/bytes.go

@@ -1,7 +1,9 @@
 package bytes
 
 import (
+	"bytes"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"strings"
 )
@@ -9,6 +11,11 @@ import (
 // The main purpose of HexBytes is to enable HEX-encoding for json/encoding.
 type HexBytes []byte
 
+var (
+	_ json.Marshaler   = HexBytes{}
+	_ json.Unmarshaler = &HexBytes{}
+)
+
 // Marshal needed for protobuf compatibility
 func (bz HexBytes) Marshal() ([]byte, error) {
 	return bz, nil
@@ -20,7 +27,8 @@ func (bz *HexBytes) Unmarshal(data []byte) error {
 	return nil
 }
 
-// This is the point of Bytes.
+// MarshalJSON implements the json.Marshaler interface. The hex bytes is a
+// quoted hexadecimal encoded string.
 func (bz HexBytes) MarshalJSON() ([]byte, error) {
 	s := strings.ToUpper(hex.EncodeToString(bz))
 	jbz := make([]byte, len(s)+2)
@@ -30,16 +38,23 @@ func (bz HexBytes) MarshalJSON() ([]byte, error) {
 	return jbz, nil
 }
 
-// This is the point of Bytes.
+// UnmarshalJSON implements the json.Umarshaler interface.
 func (bz *HexBytes) UnmarshalJSON(data []byte) error {
+	if bytes.Equal(data, []byte("null")) {
+		return nil
+	}
+
 	if len(data) < 2 || data[0] != '"' || data[len(data)-1] != '"' {
 		return fmt.Errorf("invalid hex string: %s", data)
 	}
+
 	bz2, err := hex.DecodeString(string(data[1 : len(data)-1]))
 	if err != nil {
 		return err
 	}
+
 	*bz = bz2
+
 	return nil
 }