Merkle proofs!

common/random.go

@@ -62,6 +62,10 @@ func RandUint() uint {
 	return uint(rand.Int())
 }
 
+func RandInt() int {
+	return rand.Int()
+}
+
 // Distributed pseudo-exponentially to test for various cases
 func RandUint16Exp() uint16 {
 	bits := rand.Uint32() % 16

common/test/mutate.go

@@ -0,0 +1,28 @@
+package test
+
+import (
+	. "github.com/tendermint/tendermint/common"
+)
+
+// Contract: !bytes.Equal(input, output) && len(input) >= len(output)
+func MutateByteSlice(bytez []byte) []byte {
+	// If bytez is empty, panic
+	if len(bytez) == 0 {
+		panic("Cannot mutate an empty bytez")
+	}
+
+	// Copy bytez
+	mBytez := make([]byte, len(bytez))
+	copy(mBytez, bytez)
+	bytez = mBytez
+
+	// Try a random mutation
+	switch RandInt() % 2 {
+	case 0: // Mutate a single byte
+		bytez[RandInt()%len(bytez)] += byte(RandInt()%255 + 1)
+	case 1: // Remove an arbitrary byte
+		pos := RandInt() % len(bytez)
+		bytez = append(bytez[:pos], bytez[pos+1:]...)
+	}
+	return bytez
+}